Syntheses, characterizations and electrochromic applications of polymers derived from carbazole containing thiophene rings in side chain with electrochemical and FeCl3 methods

Article abstract of DOI:10.1016/j.orgel.2012.12.023

1,8-Bis(3,6-di(thiophen-3-yl)-9H-carbazol-9-yl)octane (BDTCO) was synthesized via Ullmann and Suzuki couplings. Additionally, its homopolymer and copolymers with 3,4-ethylenedioxythiophene (EDOT), pyrrole (Py) and thiophene (Th) were synthesized and coated onto an ITO-glass surface via electrochemical oxidative polymerization. The spectroelectrochemical and electrochromic properties of the polymers were also investigated. The switching ability of these polymers was measured as the percent transmittance (T%) at their point of maximum contrast. Moreover, the polymer of BDTCO (P-BDTCO) was successfully synthesized through FeCl₃ oxidative polymerization. The compounds were characterized by FT-IR, NMR and X-ray Photoelectron Spectroscopy (XPS), and their thermal stabilities were determined via TG measurements. The solid state conductivities of the polymeric films coated onto the ITO-glass surface were measured via the four point probe technique using an electrometer. In addition, the surface morphological properties were investigated by Scanning Electron Microscopy (SEM) for different magnifications.

Full text of DOI:10.1016/j.orgel.2012.12.023

Organic Electronics 14 (2013) 730–743
Contents lists available at SciVerse ScienceDirect
Organic Electronics
journal homepage: www.elsevier.com/locate/orgel
Syntheses, characterizations and electrochromic applications
of polymers derived from carbazole containing thiophene rings
in side chain with electrochemical and FeCl3 methods
⇑
_
Aysel Aydın, Ismet Kaya
Çanakkale Onsekiz Mart University, Faculty of Sciences and Arts, Department of Chemistry, Polymer Analysis Laboratory, 17020 Çanakkale, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
1,8-Bis(3,6-di(thiophen-3-yl)-9H-carbazol-9-yl)octane (BDTCO) was synthesized via Ull-
mann and Suzuki couplings. Additionally, its homopolymer and copolymers with 3,4-eth-
ylenedioxythiophene (EDOT), pyrrole (Py) and thiophene (Th) were synthesized and coated
onto an ITO–glass surface via electrochemical oxidative polymerization. The spectroelect-
rochemical and electrochromic properties of the polymers were also investigated. The
switching ability of these polymers was measured as the percent transmittance (T%) at
their point of maximum contrast. Moreover, the polymer of BDTCO (P-BDTCO) was suc-
cessfully synthesized through FeCl3 oxidative polymerization. The compounds were char-
acterized by FT-IR, NMR and X-ray Photoelectron Spectroscopy (XPS), and their thermal
stabilities were determined via TG measurements. The solid state conductivities of the
polymeric films coated onto the ITO–glass surface were measured via the four point probe
technique using an electrometer. In addition, the surface morphological properties were
investigated by Scanning Electron Microscopy (SEM) for different magnifications.
Ó 2012 Elsevier B.V. All rights reserved.
Received 28 November 2012
Received in revised form 18 December 2012
Accepted 21 December 2012
Available online 5 January 2013
Keywords:
Electrochromism
Spectroelectrochemistry
Thermal stability
Oxidative polymerization
1. Introduction
structured co-monomers. Contrary to synthetic approach,
copolymerization is an easy and facile method to combine
Most low band gap polymers have synthesized via Su-
zuki [1–3], Yamamoto [3] and Stille [4,5] coupling poly-
merizations. Compared with these polymerization
methods, ferric (III) chloride (FeCl3) oxidative polymeriza-
tion is easy and cheap with mild reaction conditions (at
room temperature), thereby making it suitable for large
scale production [6], and gives high molecular weight
polymers. Polymerization with FeC13 has up to now been
reported to produce irregular polymers only [7]. The stan-
dard procedure is to suspend FeC13 in chloroform and then
add the thiophene monomer quickly [8]. Additionally,
the electrochromic properties of the parent polymers [12].
In literature there are several studies that investigate copo-
lymerization and tune the color of the conducting poly-
mers via copolymerization. Among that 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 varia-
tions simply between two colors, it is crucial for potential
applications to obtain a multichromic conducting polymer
with short switching time and high stability. Moreover, an
electrochromic material is one that changes color in a per-
sistent but reversible manner by an electrochemical reac-
tion, and the phenomenon is called electrochromism
[13]. A number of conjugated polymers have colors both
in the oxidized and reduced states. The color exhibited
by the polymer is determined by the band gap energy
many
p-conjugated polymers have recently been synthe-
sized via electropolymerization [9–11]. Electrocopolymer-
ization process carries out by combining with different
⇑
Corresponding author. Tel.: +90 286 218 00 18; fax: +90 286 218 05
(Eg), defined as the onset of the p–
pꢀ transition.
33.
_
E-mail address: kayaismet@hotmail.com (I. Kaya).
1566-1199/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.orgel.2012.12.023

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A. Aydın, I. Kaya / Organic Electronics 14 (2013) 730–743
731
In this paper, we primarily aimed to investigate the ef-
fects of the copolymers with pyrrole (Py), thiophene (Th)
and 3,4-ethylenedioxythiophene (EDOT) of 1,8-bis(3,6-
For BDTCO: 1H NMR (DMSO): dH ppm, 8.48 (s, 4H, Ha,
Ha0), 7.84 (s, 4H, Hd, Hd0), 7.68 (d, 4H, Hf, Hf0), 7.58 (m,
12H, Hb, Hb0, Hc, Hc0, He, He0), 4.33 (t, 2H, Hg, Hg0), 3.37
(m, 2H, Hi, Hi0), 2.52 (m, 2H, Hj, Hj0), 1.24 (m, 2H, Hk, Hk0).
di(thiophen-3-yl)-9H-carbazol-9-yl)octane
(BDTCO),
which has the aliphatic groups on electrochromic proper-
ties. Additionally, we reported electrochemically the syn-
thesis of new polymers containing carbazole moieties
with aliphatic groups, Py, EDOT and Th units. The most
widely used method is the coating of the electrode with
a monomer and then performing electropolymerization
2.3. Synthesis of the polymers
2.3.1. Synthesis of P-BDTCO by the FeCl3 oxidation method
To a suspension of FeCl3 (162 mg, 1 mmol) in chloro-
form (5 mL), compound BDTCO (77 mg, 0.1 mmol) in chlo-
roform (5 mL) was added in one portion under argon
atmosphere. The reaction was left stirring for 72 h at room
temperature. The reaction mixture was then diluted with
chloroform and washed with water. The organic phase
was then separated and stirred with ammonia (aq. 20%,
100 mL ꢂ 2) for 30 min, followed by washing with 0.2 M
ethylene-diamino-tetra-acetic acid (EDTA) solution
(50 mL ꢂ 2) and water (200 mL ꢂ 2). The solution was then
poured into methanol and the precipitate was collected by
centrifugation. After process, the polymer was obtained as
a red solid (98 mg, 65%). The synthetic route is shown in
Scheme 2 [17].
in the presence of
a co-monomer. For this purpose,
1,8-bis(3,6-dibromo-9H-carbazol-9-yl)octane (BDBCO)) was
firstly synthesized using an Ullmann coupling [14].
Then, 1,8-bis(3,6-di(thiophen-3-yl)-9H-carbazol-9-yl)octane
(BDTCO) was synthesized using a Suzuki coupling [15].
Moreover, the oxidative polymer of BDTCO (P-BDTCO)
was performed by the oxidative polymerization reaction
with ferric (III) chloride (FeCl3). The structures of the syn-
thesized polymers were confirmed by using FT-IR, 1H
NMR and CV techniques. Also, thermal stabilities of the
polymers were investigated. The conductivities of electro-
chemically prepared polymer films were measured on pel-
let at solid state for P-BDTCO and the electrode surface for
electrochemically the synthesized polymers via the four-
probe technique at room temperature. The obtained results
showed that the synthesized copolymers could be used for
electrochromic applications.
2.3.2. Electrochemical copolymerization of BDTCO with EDOT,
Py and Th
Cyclic voltammetry (CV) measurements were per-
formed using a CHI 660 C Electrochemical Analyzer at a po-
tential scan rate of 0.25 V/s. CV was employed to assay the
electrical activity of the compounds and determine their
oxidation–reduction peak potentials. Additionally, the
copolymers were separately obtained in the presence of
Th, Py and EDOT. The system consists of a CV cell contain-
ing an indium tin oxide (ITO)-coated glass plate as the
working electrode, platinum wire as the counter electrode
and Ag wire as the reference electrode. The measurements
2. Experimental section
2.1. Materials
Carbazole, N-bromosuccinimide (NBS), 1,8-dibromo-
pentane, ferric (III) chloride (anhydrous) (FeCl3) and Ali-
quat 336 were supplied from Alfa Easer Chemical Co.
(Germany). 3-Thiophene boronic acid, CuI and 18-Crown-
were performed using
a
(0.1 M) LiClO4/acetonitrile
(AN:BF3EtE) (9:1, v/v) solvent mixture at room tempera-
ture under an argon atmosphere [18]. The electropolymer-
izations involved dissolving BDTCO (1 g Lꢃ1) in 10 mL of
0.1 M AN/LiClO4:BF3EtE (9:1, v/v) and placing the resulting
solution into the CV cell before adding 4 mg of Th or Py or
EDOT. Next, the solution was repeatedly scanned in the
range of the different potentials for each measurement
(scan rate: 0.25 V/s and cycle number: 20, respectively).
The resulting copolymer and homopolymer films were
washed with AN to remove LiClO4 and BF3EtE. The homo-
polymer film of the synthesized monomer was also depos-
ited onto an ITO glass plate using a similar method for
comparison (cycle number: 20, scan rate: 0.25 V/s).
Scheme 3a and b shows the general electrocopolymeriza-
tion reaction with Py or Th or EDOT and the chemical
structures of the copolymers, respectively.
6
were supplied from Across Chemical Co. (USA).
[Pd(PPh3)4], pyrrole (Py), thiophene (Th) and 3,4-ethylene-
dioxythiophene (EDOT) were supplied from Aldrich Chem-
ical Co. (USA). SiO2, K2CO3, N,N0-dimethylacetamide (DMA),
dichloromethane (DCM), methanol, chloroform (CHCl3),
hexane, toluene, acetonitrile (AN) were supplied from
Merck Chemical Co. (Germany) and used as received. Bor-
on trifluoride ethyl etherate (BF3EtE) was supplied from
Fluka Chemical Co. Silica gel was used as an efficient and
reusable catalyst.
2.2. Syntheses of the beginning compounds and monomer
(1,8-bis(3,6-di(thiophen-3-yl)-9H-carbazol-9-yl)octane
(BDTCO))
3,6-Dibromocarbazole, the aliphatic bridged compound
with tetra Br groups (1,8-bis(3,6-dibromo-9H-carbazol-9-
yl)octane (BDBCO)) containing carbazole units and 1,8-
bis(3,6-di(thiophen-3-yl)-9H-carbazol-9-yl)octane (BDTCO)
were synthesized as reported in the literature (Yield ꢁ60%)
[10,16]. The obtained compounds have different colors. For
example, the aliphatic bridged compound with tetra Br
groups is a light yellow colored; BDTCO is a dark brown col-
ored. The synthesis pathways are shown in Scheme 1.
2.4. Structural characterization techniques
The FT-IR spectra were recorded using a Perkin Elmer
FT-IR Spectrum One via using ATR system (4000–
650 cmꢃ1). 1H NMR spectra (Bruker AC FT-NMR spectrom-
eter operating at 400 and 100.6 MHz, respectively) were
also recorded using DMSO-d6 as the solvent at 25 °C. Tetra-
methylsilane was used as an internal standard. The ob-

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A. Aydın, I. Kaya / Organic Electronics 14 (2013) 730–743
Br
Br
SiO2, NBS
2
DCM, 24 h
N
H
N
H
Br
K2 CO3, CuI
18-Crown-6
Reflux, 20 h
+
165oC
Br
S
S
Br
Br
HO
B
OH
N
N
+ 4
S
K2CO3 (aq.), [Pd(PPh3)4]
Aliquat 336
N
Toluene, 80oC, 48 h
N
Br
Br
S
S
BDBCO
BDTCO
Scheme 1. Synthesis of the compounds.
S
S
S
S
N
N
Chloroform
FeCl3
N
Ar Atm.
N
S
S
S
S
P-BDTCO
BDTCO
Scheme 2. The oxidative polymerization reaction of BDTCO with FeCl3.
tained copolymer film was characterized by X-ray Photo-
electron Spectroscopy (XPS) measurement (PHI 5000
XPS) which was carried out using mono-chromatic Al An-
ode by increasing 1 eV. A CHI 660 C Electrochemical Ana-
lyzer (CH Instruments, Texas, USA) was used to supply a
constant potential during the electrochemical syntheses
and cyclic voltammetry experiments. An Analytikjena Spe-
cord S 600 single beam spectrophotometer was used for
the spectroelectrochemical studies and characterization
of the copolymers. The electrical conductivities of electro-
chemically deposited films of the polymers on ITO-glass
plates were measured. These measurements were con-
ducted using on a Keithley 2400 Electrometer using the
four point probe technique at 25 °C. The TG-DTA data were
recorded using a Perkin Elmer Diamond Thermal Analysis
system. The compounds were scanned between 20 and
1000 °C (in N2, rate 10 °C/min). Additionally, DSC analysis
of P-BDTCO was carried out by using Perkin Elmer Pyris
Sapphire DSC. DSC measurement was performed between
25 and 420 °C (in N2, rate 20 °C/min). Scanning electron
microscopy (SEM) photographs of the compounds were re-
corded using a Philips XL-305 FEG SEM instrument.
2.5. Spectroelectrochemical studies
Both the co- and homopolymer films, which had been
electrochemically deposited onto ITO-coated glass slides,
were used to perform the spectroelectrochemical experi-
ments. Spectroelectrochemical and electrochromic mea-
surements were conducted in an LiClO4/AN solution using
an Ag wire as the reference and a Pt wire as the auxiliary
electrode. The data obtained from the cyclic voltammetry
measurements were used for the spectroelectrochemical
measurements of the copolymer and homopolymer films
[19]. These measurements were performed to account for
the absorption spectra of the copolymer and homopolymer
films under the applied potentials. A spectroelectrochemi-
cal cell includes a quartz cuvette, an Ag wire (RE), a Pt wire
and the polymer film on ITO/glass as a transparent working
electrode (WE). These measurements were performed in a

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A. Aydın, I. Kaya / Organic Electronics 14 (2013) 730–743
733
a
b
R
S
S
R:
R
O
O
or
or
S
S
S
N
H
N
N
S
N
R
Electrocopolymerization
R
N
S
S
R
R
S
S
R
S
S
R1
R2
R1
R2
S
S
N
N
N
N
R1
R2
S
S
R2
R1
R2
BDTCO-co-Th
S
BDTCO-co-Py
S
R1
S
R3
S
R3
R3
S
N
R2
R3
N
H
N
R3
O
O
S
R3
S
BDTCO-co-EDOT
S
Scheme 3. (a) Electrocopolymerization of BDTCO with Py, Th and EDOT and (b) general presentation of the copolymers.
0.1 M LiClO4 supporting electrolyte in AN, as emphasized
above.
and aromatic CAH peaks, respectively. The aliphatic and
aromatic CAH peaks are observed at 3073; 2927 and
2850 cmꢃ1, respectively, for BDBCO. The FT-IR spectrum
from BDBCO shows that the peak at 730 cmꢃ1 related to
–Br groups disappears after the reaction, as expected. Sim-
ilarly, the aliphatic and aromatic CAH peaks are observed
at 3048; 2927 and 2850 cmꢃ1, respectively, for BDTCO.
The peak at 794 cmꢃ1 and widespread peaks are differently
observed at the spectrum of BDTCO, when compared with
BDBCO. Additionally, the peak at around 1620 cmꢃ1 is re-
lated to –NH bending groups in the carbazole units. Also,
the polymer (P-BDTCO) synthesized with FeCl3 method
has the aliphatic and aromatic peaks at its spectrum. As
seen in its spectrum, the aliphatic and aromatic peaks are
obtained at 3023; 2922 and 2846 cmꢃ1, respectively. The
widespread peak at around 3200 cmꢃ1 represents the
OAH stretching vibrations due to humidity in the structure
of the monomer [22]. The peak related to CAC coupling
due to the polymerization appears at 1204 cmꢃ1, as ex-
pected (see Fig. 1a). Moreover, CAS stretching is observed
2.6. Conductivity measurements
Conductivities of the synthesized polymers were mea-
sured on a Keithley 2400 Electrometer, using four point
probe technique. Instrument was calibrated with ITO glass
plate. Iodine doping was carried out by exposure of the
polymer films to iodine vapor at atmospheric pressure in
a desiccator at 25 °C [20,21].
3. Results and discussion
3.1. Structural characterization
The FT-IR spectra of the synthesized compounds are gi-
ven in Fig. 1. Fig. 1a shows the FT-IR spectra of BDBCO,
BDTCO and P-BDTCO, which possess the aliphatic peaks

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A. Aydın, I. Kaya / Organic Electronics 14 (2013) 730–743
Fig. 1. The FT-IR spectra of (a) BDBCO, BDTCO and P-BDTCO, and (b) BDTCO-co-Th, BDTCO-co-Py and BDTCO-co-EDOT.

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A. Aydın, I. Kaya / Organic Electronics 14 (2013) 730–743
735
at 799 cmꢃ1, as reported in the literature [11,23]. Fig. 1b
shows FT-IR spectra of the electrochemically synthesized
copolymers. The FT-IR spectrum from BDTCO-co-Th shows
the following absorption peaks: 3088 cmꢃ1 (from the aro-
matic CAH stretching), 1537 and 1469 cmꢃ1 (from the
C@C stretching) and 1208 cmꢃ1 (from the CAN stretching).
The broad band observed at approximately 1648 cmꢃ1
proves the presence of polyconjugation, and the peaks at
2926 and 2850 cmꢃ1 are related to the aliphatic moieties.
The coupled CAC stretching and CAS stretching appears
at 1046 cmꢃ1 and 796 cmꢃ1, respectively. The spectrum
of BDTCO-co-Th includes the characteristic peaks like the
aliphatic and coupled CAC vibration peaks. This explains
that to be available both thiophene as co-monomer and
BDTCO as monomer in the structure of the copolymer.
Additionally, as seen in the spectrum of BDTCO-co-Py, it
shows the following absorption peaks: 3103 cmꢃ1 (from
the aromatic CAH stretching), 2941 and 2875 cmꢃ1 (from
the aliphatic CAH stretching), and 1532 cmꢃ1 (from the
C@C stretching) and 1201 cmꢃ1 (from the CAN stretching).
The coupled CAC stretching and C–S stretching appears at
1036 cmꢃ1 and 783 cmꢃ1, respectively. According to the
spectrum of BDTCO-co-EDOT, the absorption peaks are ob-
tained as follows: 3053 cmꢃ1 (from the aromatic CAH
stretching), 2962 and 2881 cmꢃ1 (from the aliphatic CAH
stretching), 1580 and 1490 cmꢃ1 (from the C@C stretching)
and 1269 cmꢃ1 (from the CAN stretching). The coupled
CAC stretching and CAS stretching appears at 1160 cmꢃ1
and 718 cmꢃ1, respectively. The intensity of the absorption
band at 718 cmꢃ1 from the CAHa stretching of the thio-
phene moiety in the monomer appear completely, which
is indicative of polymerization at the 2, and 5 positions
on the thiophene moiety in the monomer and EDOT (see
Fig 1b). Consequently, the results of these FT-IR studies
clearly indicate that copolymerization reactions with Py,
Th and EDOT and also, the polymerization process with
FeCl3 are successfully achieved.
about 284 eV is mainly due to carbon atoms belonging to
aromatic carbon groups of the polymeric conjugated back-
bone [25]. The peak at 284 eV is attributed to the CAC
bonding irrespective of the type of hybridization. Alike
C1s core level signals, N1s signal appears at around
336 eV, as expected. This peak related to N1s is assigned
to the nitrogen atoms of carbazole units. The energy posi-
tion of the nitrogen (336 eV) is indicative of CAN bonding
[26]. 2s and 2p core levels related to S atom have the sig-
nals at 227 and 152, respectively. This shows that mono-
mer units containing thiophene rings are available in the
polymer structures, as expected. Additionally, O1s signal
is observed at around 530 eV. This explains that oxidize
the polymer layer. Moreover, as seen in XPS spectrum of
the synthesized polymer, there are various contaminants
at particular ratios. For example, O1s core level is observed
at ratio of 36.5%. This is quite high in the polymer chains. It
is assumed that this peak related to O atom comes from
humidity in the structure of the polymer. Before, we
touched on humidity in the FT-IR department of the struc-
tural characterization section.
A widespread peak at
around 3200 cmꢃ1 corresponding to humidity is observed
in the FT-IR spectrum of P-BDTCO, as emphasized above.
Resultantly, the results obtained from XPS of the polymer
(P-BDTCO) are in good agreement with those from its FT-
IR spectrum.
3.2. Electrochemical properties
Thiophene derivatives readily undergo a one-electron
oxidation to form a radical cation (polaron) when their
a-positions are unsubstituted. Continual oxidation affords
higher ordered oligomers via a radical coupling mecha-
nism that ultimately forms a polymer [27]. The cyclic vol-
tammogram of P(BTDCO) in an AN/LiClO4 solvent/
electrolyte solution possesses two consecutive oxidation
peaks at 1.07 and 1.39 V, and a widespread reduction peak
at around 0.5 V when scanned from 0 to +1.8 V. This reduc-
tion has been observed for other polymers and may be due
to sequential reduction of dicationic bipolaronic charge
carriers initially to cation radical polaronic charge carriers
and then to neutral polymer or may be due to the ion
transport properties of the polymer [28]. As seen in
Fig. 4, the first oxidation peak is observed at 0.99 V. This
value shifts to 1.07 V in the repeated cycles, and a new oxi-
dation peak at 1.07 V occurs. Additionally, the second oxi-
dation peak is observed at 1.35 V and after the repeated
cycles, this value shifts to 1.30 V. A new reduction coupling
appeared at a lower potential (Eox = 0.99 V and Ered = 0.5 V),
which can be attributed to the oxidative doping (i.e., polar-
on and bipolaron formation) and reductive dedoping of the
formed polymer [29]. The decreased oxidation potential
after repeated scans is evidence of the electropolymeriza-
tion, the formation of a polyconjugated structure and a
reduction in the electrochemical band gap. The decreasing
in the peak current after repeated scans occurs because of
polymer adsorption onto the electrode surface, which
causes a sensitivity decrease in the electrode. To investi-
gate the CV behavior of BDTCO-co-Th, we performed CV
studies in the presence of thiophene between ꢃ0.2 and
+1.6 V potentials (see Fig. 4). It can be seen the voltammo-
1H NMR measurement of BDTCO is performed in DMSO
solution because of it is completely soluble in DMSO. The
molecular structure of BDTCO is also characterized by 1H
NMR spectrum using DMSO-d6 as the solvent and the 1H
NMR spectrum of BDTCO is shown in Fig. 2. As seen in
Fig. 2, it shows resonance signals for protons from the thi-
ophene, protons related to the aliphatic and benzene rings
[24]. Thiophene and carbazole groups have three signals,
respectively. According to these data, the characteristic
signals at 8.48, 7.58 and 7.56 ppm are attributed to the car-
bazole moieties, which indicate the reaction has gone to
completion. Additionally, the peaks at 7.84, 7.68 and
7.61 ppm are related to the thiophene groups and the other
characteristic peaks are the aliphatic peaks at 4.33, 3.37,
2.52 and 1.24 ppm in the monomer structure. This result
completely explains the monomer structure. According to
the obtained spectral data, the aimed product is success-
fully obtained.
In order to evaluate the surface composition state of the
synthesized polymer (P-BDTCO), XPS investigation was
carried out. Thus, intensity scale related to binding energy
levels of P-BDTCO is given in Fig. 3 and also, atomic% values
are shown as insert data in Fig. 3. As seen in Fig. 3, the sig-
nal related to C1s is observed at 284 eV. C1s component at

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A. Aydın, I. Kaya / Organic Electronics 14 (2013) 730–743
Fig. 2. 1HMR spectrum of BDTCO.
grams change drastically when compared with the voltam-
mograms related to both P(BDTCO) and thiophene [11].
According to the obtained cyclic voltammogram data, the
oxidation peaks at 0.62 and 0.12 V, and the reduction peaks
at 0.56 and 0.84 V are observed, respectively. Moreover,
there is an incremental increase at consecutive cycle num-
bers and the oxidation potential of BDTCO-co-Th and they
are different from those of either the monomer or pure thi-
ophene, as emphasized above. An incremental increase at
consecutive cycle numbers is observed in the cyclic vol-
tammogram of BDTCP-co-EDOT when scanned in the range
of ꢃ1 and +1.6 V. During the growth of the BDTCO-co-
EDOT film, the decreasing in the peak current after re-
peated scans occurs because of polymer adsorption onto
the electrode surface, which causes a sensitivity decrease
in the electrode, as emphasized above. Similarly, as seen
in the cyclic voltammogram of BDTCO-co-Py, it has one
oxidation peak at 0.49 V with one reduction peak at
ꢃ0.13 V. According to the electrochemical data obtained
from measurements, the decreased oxidation potential
after repeated scans and increases at the oxidation and
reduction peaks, that is an increase in peak intensity for
the repeated scans are evidence of electropolymerization
[30]. The experimental conditions to perform the electroc-
opolymerization reactions are chosen 20 as cycle number
and 0.25 V/s as the scan rate, respectively, for all the
measurements.
3.3. Spectroelectrochemical properties
The obtained co- and homopolymer films are different
colors on the electrode surface (see Fig. 5). The homopoly-
mer P(BDTCO) is a straw colored; BDTCO-co-Th is a fawn
colored; BDTCO-co-EDOT is a dark blue colored; BDTCO-
co-Py is a brown colored at the neutral states. In order to
investigate colors of the polymers and the spectral changes
in the range of different potentials at oxidation and reduc-
tion states are spectroelectrochemical method, that is,

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A. Aydın, I. Kaya / Organic Electronics 14 (2013) 730–743
737
Fig. 3. XPS spectrum of P-BDTCO.
Fig. 4. Cyclic voltammograms for repeated scans of P(BDTCO), BDTCO-co-Th, BDTCO-co-EDOT and BDTCO-co-Py (scan rate: 0.25 V/s, cycle numbers: 20).
examining changes in the optical properties of a polymer
on ITO upon applying a potential. It also provides informa-
tion about the properties of the conjugated polymer, such
as the band gap (Eg) and inter-gap states that appear upon
doping. Spectroelectrochemical measurements are con-
ducted at different potentials for each polymer in a 0.1 M

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A. Aydın, I. Kaya / Organic Electronics 14 (2013) 730–743
Fig. 5. Optoelectrochemical spectra of P(BDTCO), BDTCO-co-Th, BDTCO-co-EDOT and BDTCO-co-Py in the presence of 0.1 M LiClO4 in AN.
AN/LiClO4 solution. Fig. 5 shows the changes in the absorp-
wavelengths (hypsochromic shift), which corresponds to
the presence of positive carriers and the formation of fully
doped polymeric chains. As the doping level increased, the
tion spectra of P(BDTCO), BDTCO-co-Th, BDTCO-co-EDOT
and BDTCO-co-Py at various applied potentials. As the
copolymer devices oxidized, the intensities of their
p–
pꢀ
sub-gap absorption grew at the expense of the
p
pꢀ tran-
ꢃ
transitions decreased, and their charge carrier bands at
approximately 800 and 900 nm increased because of polar-
on formation [31]. Therefore, the Th, Py and EDOT copoly-
mers of BDTCO show important changes in their maximum
wavelengths. When the potential is applied in the range of
0 and +1.8 V, any changes are not observed in the absorp-
tion spectrum of P(BDTCO), but there is only a minor
change at approximately 800–900 nm, which comes from
polaron formation, as emphasized above. Resultantly,
when different potentials are applied to P(BDTCO), its
absorbance does not increase; however, this polymer is
easily electropolymerizable (see Fig. 4). Moreover, the
copolymers of Th, Py and EDOT with BDTCO have remark-
ably changes in their absorption spectra. For example,
when scanned from 0 to +1.8 V, BDTCO-co-Th exhibits
gradually an increase in the range of 600–1000 nm. On
the other hand, it is seen that the absorption peak intensity
decreases a minor reducing at around 400 nm. As seen in
the absorption spectrum of BDTCO-co-EDOT, it can be said
that the spectral changes are available at two different re-
gions. Similar to BDTCO-co-Th, when scanned from 0 to
+1.6 V, increasing the degree of oxidation in BDTCO-
co-EDOT gradually decreases the absorbance intensity at
550 nm, and simultaneously, shifts this band to longer
sition [32]. The reduced form of BDTCO-co-EDOT possesses
an absorption maximum at 580 nm, which corresponds to
an intense blue color, although the oxidized form of
BDTCO-co-EDOT possesses a violet colored. Additionally,
thin copolymer films of EDOT are transmissive blue–gray
in their oxidized state, and a highly absorbing blue–violet
in their reduced state, suggesting its use as a cathodically
coloring electrochromic material [28]. According to the
optical measurement of BDTCO-co-Py, it can be said that
the absorbance peak intensity decreases at 380 nm, and
simultaneously, the absorbance peak intensity increases
at 550 and 850 nm, when scanned from ꢃ0.6 to 1.2 V.
3.4. Electrochromic switching and the stabilities
To conduct the spectroelectrochemical measurements,
repeated scans with a cyclic voltammeter coupled to an
optical spectroscopy method are performed for various
scan cycle numbers. The potential scan range is differently
chosen for each polymer. The electrochromic switching
graphs of the polymers are given in Fig. 6. The measure-
ments are performed using a single wavelength with obvi-
ously changing absorption intensity for BDTCO-co-EDOT
and P(BDTCO) and also, two wavelengths are used for

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A. Aydın, I. Kaya / Organic Electronics 14 (2013) 730–743
739
Fig. 6. Electrochromic switching of the optical absorbances of BDTCO-co-Py at 370 and 900 nm, BDTCO-co-EDOT at 580 nm, and P(BDTCO) at 700 nm in the
presence of 0.1 M LiClO4 in AN.
BDTCO-co-Py. A scan rate of 0.05 V/s is chosen. During the
switching experiment, the kmax values are chosen as 370
and 900, 580 nm and 700 nm for BDTCO-co-Py, BDTCO-
co-EDOT and P(BDTCO), respectively. The polymer films
are deposited onto the ITO-coated glass slides under con-
stant potential conditions, as mentioned above, and their
absorbances are monitored at kmax while switching be-
tween potentials. As shown in Fig. 6, during the repeated
potential scans, the absorption intensity of BDTCO-co-Py
is clearly stable between ꢃ0.6 V and 1.2 V at 370 and
900 nm for two wavelengths. The response time for
BDTCO-co-Py from the neutral (ꢃ0.6 V) to the oxidized
(1.2 V) states is found to be 25 s at 370 nm and 24 s at
900 nm, respectively. BDTCO-co-EDOT also has good
absorption recoveries at the applied potentials, which indi-
ing the switching process, the percent transmittance (T%)
is recorded using a UV–Vis spectrophotometer. The optical
contrast (DT%) was measured as the difference between
the T% values recorded for the neutral and oxidized poly-
mer films and found to be 14% at 370 nm and 17% at
900 nm for BDTCO-co-Py, 44% at 580 nm for BDTCO-co-
EDOT and 20% at 700 nm for P(BDTCO). The electrochromic
switching measurement of BDTCO-co-Th could not be per-
formed due to its film is not successfully coated onto ITO;
however, this polymer is easily electropolymerizable and
the optical changes can be seen in its spectrum according
as variable potential (see Figs. 4 and 5). As a result of their
aliphatic-substituted molecular structures, the monomer
and polymer chains can be further separated from each
other to diminish the effects of aggregation. Therefore,
the dopant ions can move more freely into and out of the
space between the polymer chains in the electrochromic
material during redox switching. In addition, Reynolds
and Sankaran found that alkyl – substituted polymers of
EDOT (PEDOT-C8 and PEDOT-C14) exhibited improved
electrochromic performances relative to unsubstituted
PEDOT. They reported that PEDOT-C14 in the oxidized film
was 60% transmissive, whereas the reduced film was <5%
cates the percent transmittance (DT%) at 580 nm. The sta-
bility of the redox states during the scans is the most
property for an electro-active polymer to be useful in con-
structing new electrochromic devices [33–37]. The re-
sponse time for BDTCO-co-EDOT from the neutral
(ꢃ1.0 V) to the oxidized (1.6 V) state is found to be 27 s
at 580 nm. The ability of a material to exhibit a noteworthy
color change is important for electrochromic applications.
The electrochemically synthesized polymers on ITO-glass
have brown colors in the neutral states and also, both blue
and green colors in the oxidized states. As seen in Fig. 5, the
response time for P(BDTCO) from the neutral (0.0 V) to the
oxidized (1.8 V) states is found to be 25 s at 700 nm. Dur-
transmissive (DT% = 55%) [28]. Therefore, the transmit-
tances of the polymeric structures can be low because of
the effects of aliphatic groups.
Fig. 7 presents the changes in the anodic and cathodic
peak currents as a function of the potential. The scan rate

_
740
A. Aydın, I. Kaya / Organic Electronics 14 (2013) 730–743
Fig. 7. Cyclic voltammograms of P(BDTCO) and BDTCO-co-EDOT as a function of repeated scans 0.05 V/s after 14 cycles for P(BDTCO) and BDTCO-co-EDOT.
is chosen as 0.05 V/s. The polymers show only a slight de-
crease in electroactivity accompanied by unperturbed col-
or change after 14 cycles for P(BDTCO) and BDTCO-co-
EDOT. This result reveals that the synthesized copolymers
have reasonable environmental and redox stability [18].
Therefore, the polymers can be operated with different ap-
plied potentials for future electrochromic applications.
curves indicate that endothermic and exothermic peak
for BDTCO at 176 and 837 °C, respectively. At the same
time, losses of the solvent occur as 1.29% for BDTCO,
4.89% for P-BDTCO, 8.02% for BDTCO-co-Th and 3.59% for
BDTCO-co-EDOT at the range of 20 and 120 °C. DSC analy-
sis of P-BDTCO is performed (see Fig. 8b). The glass transi-
tion temperature (Tg) of the polymer is also calculated from
its DSC curve and it is found as 132 °C. Also, the change of
the specific heat (DCp) during the glass transition is calcu-
3.5. Thermal stability
lated, and found as 3.124 ꢂ 10ꢃ3 J/g °C. The calculated re-
gion is shown as insert figure of Fig. 8b by enlarging, and
therefore this peak can be clearly seen. Resultantly, due
to the synthesized compounds have high thermal stabili-
ties; they can be promising candidates for aerospace
applications.
The thermal degradation data (TGA, DTG and DTA) for
the compounds are summarized in Table 1, TG curves for
the compounds and DSC curve of P-BDTCO are shown in
Fig. 8a and b, respectively. According to TG and DTG re-
sults, the compounds have different degradation steps.
Additionally, the initial degradation temperatures (Ton) of
the compounds are at around 160 °C, except BDTCO-co-
EDOT, which has quite high the initial degradation temper-
ature. This result shows that it is thermally stable. More-
over, temperature values corresponding to weight losses
of 20% and 50% are given in Table 1 for each compound,
respectively. The char from BDTCO, P-BDTCO, BDTCO-co-
Th and BDTCO-co-EDOT is 27.00%, 48.00%, 6.50% and
4.00%, respectively, at 1000 °C. According to these results,
the polymer synthesized with FeCl3 has higher carbine res-
idue amount than those of the others. Tmax values are
clearly determined from the DTG curves, and also DTA
3.6. Conductivity measurements
The conductivity measurements of the polymers are
performed via the four-probe technique at room tempera-
ture. While the conductivities of electrochemically pre-
pared polymer films are measured on the electrode
surface, the conductivity measurement of P-BDTCO is mea-
sured on its pellet at solid state. When the polymer films
coated on ITO/glass are exposed to iodine vapor, no struc-
tural changes from iodine complexation are observed for
the polymers, and their conductivities are, therefore, stable
Table 1
Thermal degradation values of the compounds.
Compounds
TGA (°C)
DTA (°C)
a
b
c
d
Ton
Tmax
T20,
T50
,
% Char at 1000 °C
Losses of solvent,% 20–120 °C
Exo
Endo
BDTCO
P-BDTCO
BDTCO-co-Th
BDTCO-co-EDOT
158
163
165
247
171, 457, 685, 844
260, 784
277, 696, 930
334, 467
304
372
274
273
875
819
553
348
27.00
48.00
6.50
1.29
4.89
8.02
3.59
837
–
–
176
–
–
4.00
–
–
a
b
c
The onset temperature.
Temperature of the peak maxima.
Temperature corresponding to 20% weight loss.
Temperature corresponding to 50% weight loss.
d

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A. Aydın, I. Kaya / Organic Electronics 14 (2013) 730–743
741
Fig. 8. (a) TG curves of the compounds and (b) DSC curve of P-BDTCO.
(see Table 2). But, increasing conductivity of P-BDTCO is
obtained via iodine doping and the pellet of P-BDTCO is ex-
posed to iodine vapor during 5 days. As a result, its initial
conductivity or conductivity at the undoped state is found
as 3 ꢂ 10ꢃ9 S cmꢃ1. After the doping reaction for 120 h
with iodine vapor the conductivity of P-BDTCO nearly in-
creases as 667 times of the initial conductivity (up to
2 ꢂ 10ꢃ6 S cmꢃ1). Being low of its initial conductivity value
is related to the aliphatic groups. This decrease is assumed
to be caused by the aliphatic groups which substituted on
I
I
I
I
I
I
I
I
I
S
S
N
N
S
Table 2
I
I
I
Conductivities of the polymers.
I
I
I
Conductivity (S cmꢃ1
)
S
Compounds
3.00 ꢂ 10ꢃ9 (undoped state)
2.00 ꢂ 10ꢃ6 (doped state)
4.50 ꢂ 10ꢃ5
I
I
I
P-BDTCO
S
BDTCO-co-Th
BDTCO-co-Py
BDTCO-co-EDOT
1.60 ꢂ 10ꢃ5
2.30 ꢂ 10ꢃ4
Scheme 4. Possible complex form of P-BDTCO with Iꢃ3 molecule.

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742
A. Aydın, I. Kaya / Organic Electronics 14 (2013) 730–743
Fig. 9. SEM photographs of BDTCO with (a) 50 lm, (b) 10 lm, (c) 5 lm particle magnifications and P-BDTCO with (d) 50 lm, (e) 10 lm and (f) 5 lm particle
magnifications, respectively.
the carbazole nitrogen. Length of these aliphatic groups af-
fect to intermolecular electron transfer. Also, these ali-
phatic groups hinder the coordination of Iꢃ3 with
carbazole nitrogen, because of the steric effect exerted by
them. Since nitrogen is a very electronegative element
and is capable of coordinating with the Iꢃ3 , Diaz et al. sug-
gested a conductivity mechanism when doped with iodine
[38]. Furthermore; it is believed that iodine doping occurs
not only on the carbazole nitrogen atoms but also on the
thiophene rings. Similarly, sulfur in the thiophene rings is
a very electronegative element and is capable of coordinat-
ing with the Iꢃ3 , as emphasized above. The conductivity at
doped state is high because of coordinating of thiophene
rings with the Iꢃ3 molecule [39]. The conductivity mecha-
nism over the polymer backbone can be proposed as
Scheme 4.
3.7. Surface morphology
Morphological properties of BDTCO and P-BDTCO are
obtained by scanning electron microscopy (SEM) tech-
nique. SEM photographs of powder forms are given in
Fig. 9 at different magnifications. According to the SEM
images, the surface of BDTCO has different sized unhomog-

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A. Aydın, I. Kaya / Organic Electronics 14 (2013) 730–743
743
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enous particles with sharp edges. These sharp edges are
probably because of the aliphatic groups in the monomer
structure. As seen in Fig. 9c, SEM photograph of BDTCO
has vertically platy layers. Also, SEM photographs of the
polymer (P-BDTCO) synthesized with FeCl3 are given in
Fig. 9d–f, respectively, at different magnifications. As
investigated its SEM images, it can be seen that P-BDTCO
is an agglomerate form (see Fig. 9d). Fig. 9f has a collected
material surface like collapsing of dried foliages. Moreover,
when compared with BDTCO, P-BDTCO is different from it
at the same magnifications.
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4. Conclusion
According to the spectroelectrochemical measure-
ments, the synthesized copolymers exhibited the electro-
chromic properties, can be tunable to different colors like
straw and violet colors. Spectroelectrochemical analysis
of P(BDTCO) was performed at different potentials but no
changes in its optical absorbance was observed; however,
this material was easily electropolymerizable and also, it
had fairly well film stability. Conductivity measurements
demonstrated that these polymers were semi-conducting.
This result can be explained by the presence of the ali-
phatic groups in the polymer structures, which decreases
conductivity. In addition, increased conductivity of P-
BDTCO and the maximal conductivity for P-BDTCO were
obtained via iodine doping when exposed to iodine vapor.
As a result, P-BDTCO could also be useful materials in elec-
tronic or optoelectronic studies by doping with iodine for a
long time. The resultant data showed that the electro-
chemically synthesized copolymers could be used in elec-
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Acknowledgement
The authors would like to thank Government Planning
Organization for the financial support (Project No:
GPO2010K120710).
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