Synthesis and characterization of yellow and green light emitting novel polymers containing carbazole and electroactive moieties

Article abstract of DOI:10.1016/j.electacta.2012.01.028

The compounds 1,5-bis(3,6-di(thiophen-3-yl)-9H-carbazol-9-yl)pentane (B1) and 1,2-bis(2-(3,6-di(thiophen-3-yl)-9H-carbazol-9-yl)ethoxy)ethane (B2) were synthesized via Ullmann and Suzuki couplings. Additionally, the homopolymers and copolymers of these compounds with 3,4-ethylenedioxythiophene (EDOT) and thiophene (Th) were synthesized and coated onto an ITO-glass surface via electrochemical oxidative polymerization. The spectroelectrochemical and electrochromic properties of these compounds were also investigated. The switching ability of these polymers was measured as the percent transmittance (%T) at their point of maximum contrast. The solid state electrical conductivities of the polymeric films coated onto the ITO-glass surface were measured via the four point probe technique using an electrometer. The compounds were characterized by FT-IR and NMR, and their thermal stabilities were determined via TG measurements. Fluorescence measurements were performed using DMSO solutions, and the synthesized polymers emitted both green and yellow colors based on the tuning of the excitation wavelength, which indicates that these polymers could be used to produce new polymeric light emitting diodes (PLEDs) with green and yellow emissions.

Full text of DOI:10.1016/j.electacta.2012.01.028

Electrochimica Acta 65 (2012) 104–114
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Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Synthesis and characterization of yellow and green light emitting novel polymers
containing carbazole and electroactive moieties
∗
˙
Aysel Aydın, Ismet Kaya
C¸ anakkale Onsekiz Mart University, Faculty of Sciences and Arts, Department of Chemistry, 17020, C¸ anakkale, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
The compounds 1,5-bis(3,6-di(thiophen-3-yl)-9H-carbazol-9-yl)pentane (B1) and 1,2-bis(2-(3,6-
di(thiophen-3-yl)-9H-carbazol-9-yl)ethoxy)ethane (B2) were synthesized via Ullmann and Suzuki
couplings. Additionally, the homopolymers and copolymers of these compounds with 3,4-
ethylenedioxythiophene (EDOT) and thiophene (Th) were synthesized and coated onto an ITO-glass
surface via electrochemical oxidative polymerization. The spectroelectrochemical and electrochromic
properties of these compounds were also investigated. The switching ability of these polymers was mea-
sured as the percent transmittance (%T) at their point of maximum contrast. The solid state electrical
conductivities of the polymeric films coated onto the ITO-glass surface were measured via the four point
probe technique using an electrometer. The compounds were characterized by FT-IR and NMR, and their
thermal stabilities were determined via TG measurements. Fluorescence measurements were performed
using DMSO solutions, and the synthesized polymers emitted both green and yellow colors based on the
tuning of the excitation wavelength, which indicates that these polymers could be used to produce new
polymeric light emitting diodes (PLEDs) with green and yellow emissions.
Received 20 October 2011
Received in revised form 5 January 2012
Accepted 6 January 2012
Available online 15 January 2012
Keywords:
Electropolymerization
Thiophene
Carbazole
Spectroelectrochemistry
©
2012 Elsevier Ltd. All rights reserved.
1
. Introduction
methods that including copolymerization with the bonding of
certain functional groups [8–12] modified with electro-active moi-
eties, such as thiophene [13], fluorine [14], carbazole and pyrrole.
These compounds have been used to form electrochromic poly-
mers with useful properties for their various applications [15,16].
A great deal of attention has focused on conducting polymers
because of the broad range of their common electrochromic appli-
cations, such as for various types of sensors, LEDs, actuators
and electrochromic devices [17]. Electrochromic properties have
proven especially promising for constructing mirrors [18], displays
[19,5,20] windows [21–23], and earth-tone chameleon materials
[24,25]. Electrochromic rear- and side-view mirrors based on this
concept have been recently commercialized in the automotive
industry [26,27].
In this study, we primarily aimed to investigate the effects of
alkyl and ether groups on electro chromic properties. Additionally,
we reported the synthesis of new polymers containing carbazole,
EDOT and thiophene units. For this purpose, 1,5-bis(3,6-dibromo-
9H-carbazol-9-yl)pentane (A1) and 1,2-bis(2-(3,6-dibromo-9H-
carbazol-9-yl)ethoxy)ethane (A2) were first synthesized using an
Ullmann coupling [28]. Then, 1,5-bis(3,6-di(thiophen-3-yl)-9H-
carbazol-9-yl)pentane (B1) and 1,2-bis(2-(3,6-di(thiophen-3-yl)-
Electrochromism refers to the reversible color change of
an electroactive material through an electrochemical redox
reaction. Electrochromic polymers have received increasing atten-
tion because of their potential for structurally controllable
HOMO–LUMO band gaps, rapid switching speeds, high contrast
capabilities, and ease of processing [1–3]. These properties give the
polymers advantage over inorganic electrochromic materials. The
optical changes in these electrochromic polymers are caused by the
low electrical current induced by small potentials on the order of
a fraction of a volt to a few volts, and their color is determined by
their band gap, which is defined as the onset of the ␲–␲* transi-
tion [4]. Therefore, controlling the band gap becomes an important
issue for constructing dual-polymer based electrochromic devices,
which match a lower band gap polymer (cathodic coloring) to a
higher band gap polymer (anodic coloring) to obtain a high degree
of contrast for the switching process [5]. Materials with more than
two redox states may electrochemically exhibit several colors and
are referred to as poly-electrochromic [6].
Many semi-conducting polymers have recently been synthe-
sized via electropolymerization [7]. Some of these syntheses
9
H-carbazol-9-yl)ethoxy)ethane (B2) were synthesized using a
1
13
Suzuki coupling [29]. UV–Vis, FT-IR, both H and C NMR and CV
were used for structural characterization. The fluorescence charac-
teristics of the obtained polymeric compounds were investigated
∗
Corresponding author. Tel.: +90 286 218 00 18; fax: +90 286 218 05 33.
E-mail address: kayaismet@hotmail.com ( I˙ . Kaya).
0
013-4686/$ – see front matter © 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2012.01.028

A. Aydın, I˙ . Kaya / Electrochimica Acta 65 (2012) 104–114
105
in solution. The synthesized polymers possessed fluorescent ten-
dencies indicative of green and yellow light emissions, which is
important for organic light emitting diode (OLED) and polymeric
light emitting diode (PLED) applications.
solution was poured into 100 ml of methanol. The precipitated
crude product was then collected as a brown solid and washed
three times with a methanol and water mixture (1:1, v/v). The
◦
obtained products were dried in a vacuum oven at 60 C [33].
(
Yields: 65, 50, 62 and 46% for A1, B1, A2 and B2, respectively.)
−
1
2
. Experimental
A1: FT-IR (cm ): v(C H aromatic) 3068 m, v(C H aliphatic)
928, 2859 m, v(C C phenyl) 1590, 1568s, v(C N) 1286s, v(C Br)
2
1
ꢀ
2.1. Materials
799 s. H NMR (DMSO): ıH ppm, 8.46 (s, 4H, Hf, Hf ), 7.55 (d, 4H,
Hd, Hd ), 7.51 (d, 4H, He, He , J = 9.54 Hz), 4.32 (t, 4H, Hc, Hc ,
ꢀ
ꢀ
ꢀ
d
ꢀ
Carbazole, N-bromosuccinimide (NBS), 1,5-dibromopentane,
Jt = 2.92 Hz), 1.74 (m, 4H, Hb, Hb , Jm = 1.74 Hz), 1.26 (m, 2H, Ha).
1
3
Aliquat 336 and 1,2-bis(2-chloroethoxy)ethane were supplied
from Alfa Aesar Chemical Co. (Germany). 3-thiophene boronic
acid, CuI and 18-Crown-6 were supplied from Acros Chem-
ical Co. (Germany). [Pd(PPh ) ], thiophene (Th) and 3,4-
C NMR (DMSO-d6): ıH ppm, 139.00 (C1), 134.11 (C2), 128.74 (C3),
122.85 (C4), 117.19 (C5), 109.81 (C6), 54.09 (C7), 30.82 (C8), 23.37
(C9).
B1: FT-IR (cm 1): v(C H aromatic) 3053 m, v(C H aliphatic)
−
3
4
1
ethylenedioxythiophene (EDOT) were supplied from Aldrich
2925 m, v(C C phenyl) 1591, 1470s, v(C N) 1204s, v(C S) 795 s. H
ꢀ
ꢀ ꢀ
NMR (DMSO-d6): ıH ppm, 8.46 (s, 4H, Hf, Hf ), 7.85 (s, 4H, Hi, Hi ),
Chemical Co. (Germany). SiO , K CO , N,N -dimethylacetamide
2
2
3
ꢀ ꢀ
7.69 (d, 4H, Hh, Hh , Jd = 7.56 Hz), 7.55 (d, 4H, Hd, Hd , Jd = 8.03 Hz),
(
DMA), dichloromethane (DCM), methanol, chloroform (CHCl ),
3
ꢀ
ꢀ
ꢀ
hexane, toluene, acetonitrile (AN) and dimethylsulfoxide (DMSO)
were supplied from Merck Chemical Co. (Germany) and used as
received. Silica gel was used as an efficient and reusable catalyst.
7.50 (d, 4H, He, He ), 6.89 (d, 4H, Hg, Hg ), 4.32 (t, 4H, Hc, Hc ,
ꢀ
Jt = 3.03 Hz), 1.75 (m, 4H, Hb, Hb , Jm = 1.50 Hz), 1.25 (m, 2H, Ha).
C NMR (DMSO-d6): ıH ppm, 144.97 (C1), 140.44 (C2), 134.78 (C3),
13
1
29.39 (C4, C5), 124.19 (C6), 119.45 (C7), 117.70 (C8, C9), 111.14
2.2. Synthesis of 3,6-dibromocarbazole
(C10), 53.56 (C11), 31.72 (C12), 26.61 (C13).
A solution of NBS (1.78 g, 10 mmol) in DCM (150 ml) was added
2.4. Electrochemical polymerization of 1,5-bis(3,6-di(thiophen-
3-yl)-9H-carbazol-9-yl)pentane (B1) and 1,2-bis(2-(3,6-di
(thiophen-3-yl)-9H-carbazol-9-yl)ethoxy)ethane (B2)
drop-wise to a stirred mixture of carbazole (0.835 g, 5 mmol) in
DCM (100 ml) containing 20 g of silica. This reaction mixture was
stirred for 24 h in the absence of light at room temperature. The
reaction mixture was then filtered and the silica was washed with
DCM (3 × 30 ml). The combined extracts were then washed with
Cyclic voltammetry (CV) measurements were performed using
a CHI 660 C Electrochemical Analyzer at a potential scan rate of
0.25 V/s. CV was employed to assay the electrical activity of the
compounds and determine their oxidation–reduction peak poten-
tials. Additionally, the copolymers were measured in the presence
of Th and EDOT. The system consists of a CV cell containing an
indium tin oxide (ITO)-coated glass plate as the working elec-
trode, platinum wire as the counter electrode and Ag wire as the
reference electrode. The measurements were performed using a
(0.1 M) LiClO /acetonitrile (AN:BF EtE) (9:1, v/v) solvent mixture
◦
water (200 ml) and dried in a vacuum oven at 60 C [30] (Yield:
7
5%).
2
.3. Synthesis of the alkyl and ether bridging carbazole monomer
Two primary synthesis methods were commonly used to
synthesize both 1,5-bis(3,6-di(thiophen-3-yl)-9H-carbazol-9-
yl)pentane (B1) and 1,2-bis(2-(3,6-di(thiophen-3-yl)-9H-
4
3
carbazol-9-yl)ethoxy)ethane (B2), as shown in Scheme 1.
The first procedure involved the initial synthesis of
at room temperature under an argon atmosphere [34]. The elec-
−
1
tropolymerizations involved dissolving either B1 or B2 (1 g L ) in
10 ml of 0.1 M AN/LiClO :BF EtE (9:1, v/v) and placing the resulting
1
,5-bis(3,6-dibromo-9H-carbazol-9-yl)pentane (A1) and 1,2-bis(2-
4
3
(
3,6-dibromo-9H-carbazol-9-yl)ethoxy)ethane (A2), whereas
solution into the CV cell before adding 4 mg of Th or EDOT. Next,
the solution was repeatedly scanned between -0.4 and 1.5 V (scan
rate: 0.25 V/s; cycle number: 20 and 100, respectively). The result-
ing copolymer and homopolymer films were washed with AN to
the second procedure involved the separation of bromine
and boronic acid groups. 1,5-bis(3,6-dibromo-9H-carbazol-9-
yl)pentane (A1) was synthesized from 1,5-dibromopentane and
3
,6-dibromocarbazole according to the method reported in the
remove LiClO4 and BF EtE. The homopolymers of the synthesized
3
literature [31]. CuI (0.0071 g, 0.0375 mmol), 18-Crown-6 (0.0033 g,
monomers were also deposited onto an ITO glass plate using a sim-
ilar method for comparison (cycle number: 20, scan rate: 0.25 V/s)
(Scheme 2).
0
.0125 mmol), K CO3 (0.207 g, 1.5 mmol), 3,6-dibromocarbazole
2
ꢀ
(
0.4875 g, 1.5 mmol) and N,N -dimethylacetamide (DMA) (5 ml)
were added to a round-bottom flask and vigorously stirred at
◦
1
65 C under argon. After 2 h, a solution of 1,5-dibromopentane
2.5. Structural characterization
(
0.1725 g, 0.75 mmol) in hot DMA (10 ml) was added to this mixture
slowly before heating to reflux for 20 h. This reaction solution was
poured into 200 ml of water and the precipitated crude product
The FT-IR spectra were recorded using a Perkin Elmer FT-IR
−
1
1
13
Spectrum One via using ATR system (4000–650 cm ). H and
C
was collected, dried and re-crystallized from CHCl /hexane (1:1).
The pure compounds were obtained as a straw-colored solid.
NMR spectra (Bruker AC FT-NMR spectrometer operating at 400
and 100.6 MHz, respectively) were also recorded using DMSO-d6
as the solvent at 25 C. Tetramethylsilane was used as an internal
3
◦
1
,2-bis(2-(3,6-dibromo-9H-carbazol-9-yl)ethoxy)ethane
(A2)
was similarly synthesized from 1,2-bis(2-chloroethoxy)ethane
and 3,6-dibromocarbazole [32]. The synthetic routes for these
compounds are shown in Scheme 1. For the second step, 3-
standard. A CHI 660 C Electrochemical Analyzer (CH Instruments,
TX, USA) was used to supply a constant potential during the elec-
trochemical syntheses and cyclic voltammetry experiments. An
Analytikjena Specord S 600 single beam spectrophotometer was
used for the spectroelectrochemical studies and characterization
of the polymers. The electrical conductivities of electrochemically
deposited films of the polymers on ITO-glass plates were mea-
sured. These measurements were conducted using on a Keithley
thiophene boronic acid (0.12 g, 0.9 mmol), 3 ml of 2 M K CO3 (aq.),
2
[
Pd(PPh ) ] (0.069 g, 0.06 mmol), two drops of both Aliquat 336
3 4
and either 1,5-bis(3,6-dibromo-9H-carbazol-9-yl)pentane (A1)
0.1436 g, 0.2 mmol) or 1,2-bis(2-(3,6-dibromo-9H-carbazol-9-
(
yl)ethoxy)ethane (A2) (0.1528 g, 0.2 mmol) and toluene (6 ml)
◦
were added to a round-bottom flask and vigorously stirred at
2400 Electrometer using the four-point probe technique at 25 C.
A Shimadzu RF-5301PC spectrofluorophotometer was used for the
◦
8
0 C under argon. After 48 h, the reaction was complete, and the

1
06
A. Aydın, I˙ . Kaya / Electrochimica Acta 65 (2012) 104–114
Scheme 1. General synthesis for A1, A2, B1, and B2.
fluorescence measurements. The TG-DTA data were obtained using
a Perkin Elmer Diamond Thermal Analysis system. The compounds
a Pt wire as the auxiliary electrode. The data obtained from the
cyclic voltammetry measurements were used for the spectroelec-
trochemical measurements of the copolymer and homopolymer
films [35]. These measurements were performed to account
for the absorption spectra of the copolymer and homopolymer
films under the applied potentials. The spectroelectrochemi-
cal cell included a quartz cuvette, an Ag wire (RE), a Pt wire
counter electrode (CE) and the polymer film on ITO/glass as
a transparent working electrode (WE). These measurements
were performed in a 0.1 M LiClO4 supporting electrolyte in
AN.
◦
◦
were measured between 20–1000 C (in N , rate 10 C/min).
2
2.6. Spectroelectrochemical characterization
Both the co- and homopolymer films, which had been elec-
trochemically deposited onto ITO-coated glass slides, were used
to perform the spectroelectrochemical experiments. Spectroelec-
trochemical and electrochromic measurements were conducted
in an LiClO /AN solution using an Ag wire as the reference and
4

A. Aydın, I˙ . Kaya / Electrochimica Acta 65 (2012) 104–114
107
Scheme 2. Copolymerization of B1 and B2 with Th and EDOT.
1
2.7. Fluorescence measurements
The H NMR spectrum of D1 (Scheme 3) possesses the following
peaks: 8.14 (d, 4H, Ha), 7.97 (d, 4H, Hb), 7.22 (s, 4H, Hc), 7.09 (s, 4H,
Hd), 6.96 (s, 4H, He), 5.34 (s, 4H, Hf), 4.36 (d, 4H, Hg), 3.74 (t, 2H,
Hi), 2.06 (m, 2H, Hj), 1.25 (m, 2H, Hk). The decreased intensity of
the ␣-hydrogen peak confirmed the polymerization through the 2
and 5 positions on the thiophene moiety of the monomer [37].
The FT-IR spectra of the synthesized compounds are given in
Fig. 2a shows the FT-IR spectrum of 3,6-dibromocarbazole, which
possesses an NH stretching peak and aromatic C H peak at 3419
A Shimadzu RF-5301PC spectrofluorophotometer was used for
the fluorescence measurements. The emission and excitation spec-
tra of D1 and P(B2) were obtained after the copolymer and
homopolymer films on the ITO-coated glass were dissolved in
DMSO. The photographs of these compounds in a DMSO solution
were taken at 400 nm under daylight.
−
1
and 3064 cm , respectively. The FT-IR spectrum from A1 shows
that the NH peak disappears after the reaction. The FT-IR spec-
3
. Results and discussion
−
1
trum from P(B2) shows the following absorption peaks: 3063 cm
−
1
3
.1. NMR spectra and FT-IR spectra
(from the aromatic C H stretching), 1590 and 1471 cm
(from
the C C stretching) and 1289 cm 1 (from the C N stretching). The
−
The obtained co- and homopolymer films are different colors on
the electrode surface. A1, B1 and D1 are soluble in polar organic sol-
vents, such as DMSO, and insoluble in other solvents. The 1H NMR
spectra of A1 and B1 were obtained and are shown in Fig. 1a and b
shows resonance signals for protons from the thiophene, CH2 and
benzene rings [36]. The molecular structures of A1 and B1 were
also characterized by 1H and C NMR spectra using DMSO-d6 as
the solvent. The characteristic signals at 8.46, 7.56, 7.54, 7.52 and
13
7
.50 ppm were attributed to the carbazole moiety, which indicates
the reaction had gone to completion. Additionally, the aliphatic
peaks at 4.32, 1.74 and 1.26 ppm were from the monomer structure.
This result completely explains the monomer structure. For B1, new
peak signals were observed in the spectrum and attributed to the
thiophene groups, which have peaks at 7.85, 7.69 and 6.89 ppm.
When the peaks for A1 are compared with those for B1, a few dif-
ferences are normally observed. Furthermore, these changes can be
1
3
13
see in the C NMR spectrum of B1. For the C NMR spectrum of
B1, the coupling values shifted to 144.97 and 140.44 ppm because
of the C C couplings in the structure. The C C coupling peaks
of the thiophene and carbazole units were monitored at nearby
−1
1
200–1000 cm in FT-IR spectrum. Therefore, the coupled carbons
in the structure have lower electron densities and higher chemical
shifts.
Scheme 3. The structure of D1.

1
08
A. Aydın, I˙ . Kaya / Electrochimica Acta 65 (2012) 104–114
Fig. 1. 1HMR spectra of (a) A1, and (b) B1.
broad band observed at approximately 1623 cm−1 proves the pres-
The cyclic voltammograms of C2 possessed two consecutive oxi-
dation peaks at 0.85 V as well as two reduction peaks at 0.74 and
1.05 V when scanned between 0 and +1.3 V. During the growth of
the C2 film, a new reduction coupling appeared at a lower poten-
tial (Eox = 0.85 V and Ered = 0.74 V), which can be attributed to the
oxidative doping (i.e., polaron and bipolaron formation) and reduc-
tive dedoping of the formed polymer [31]. Cyclic voltammograms
of P(B1) and C1 are shown in Fig. 3b. As seen in Fig 3b, P(B1) has two
reversible oxidation peaks at 0.84 and 1.17 V with reduction peaks
at 0.70 and 1.01 V. As homopolymer P(B1) coated the ITO, it also dis-
solved into the CV cell. Additionally, the surface of the monomer
film was quite thin. Therefore, its CV behavior could be only inves-
tigated, but any spectroscopic activity cannot be observed. The
decreased oxidation potential after repeated scans is evidence of
electropolymerization. The CV behavior of C1 showed an increase
in peak intensity for the repeated scans [36].
−
1
ence of polyconjugation, and the peaks at 2920 and 2865 cm
were related to the CH CH2 moiety. The coupled C C stretching
2
−1
−1
and C S stretching appears at 1090 cm and 724 cm , respec-
tively. The intensity of the absorption band at 799 cm from the
Ha stretching of the thiophene moiety in the monomer disap-
−
1
C
peared completely, which is indicative of polymerization at the 2,
and 5 positions on the thiophene moiety in the monomers. The FT-
IR spectra from the copolymers are shown in Fig. 2b. The results
of these FT-IR studies clearly indicated that copolymerization was
successfully achieved.
3.2. Cyclic voltammetry
Thiophene derivatives readily undergo a one-electron oxidation
to form a radical cation (polaron) when their ␣-positions are unsub-
stituted. Continual oxidation affords higher ordered oligomers
via a radical coupling mechanism that ultimately forms a poly-
mer [38]. The cyclic voltammograms of P(B2) in an AN/LiClO4
solvent/electrolyte solution possessed two consecutive oxidation
peaks at 0.65 and 1.10 V and two reduction peaks at 0.57 and 0.93 V
when scanned from 0 to +1.6 V. As seen in Fig. 3a, the first oxi-
dation peak was observed at 1.03 V. This value shifts to 0.65 V in
the repeated cycles, and a new oxidation peak occurs at 1.10 V.
The decreased oxidation potential after repeated scans is evidence
of the electropolymerization, 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 investigate the CV behav-
ior of D2, we performed CV studies in the presence of EDOT using
the same experimental conditions as above (Fig. 3a). The voltam-
mograms changed drastically, and both the incremental increase
between the consecutive cycle numbers and the oxidation poten-
tial of D1 differed from those of either the monomer or pure EDOT.
3.3. Spectroelectrochemical properties
Spectroelectrochemistry is
a good method for examining
changes in the optical properties of a polymer on ITO upon apply-
ing a potential. It also provides information about the properties
of the conjugated polymer, such as the band gap (Eg) and intergap
states that appear upon doping. Spectroelectrochemical measure-
ments were conducted at different potentials for each polymer in a
0.1 M AN/LiClO4 solution. Fig. 4a shows the changes in the absorp-
tion spectra of P(B2), C2 and D2 at various applied potentials. As
the copolymer devices oxidized, the intensities of their ␲–␲* tran-
sitions decreased, and their charge carrier bands at approximately
800–900 nm increased because of polaron formation [39]. There-
fore, the Th and EDOT copolymers of B2 show important changes in
their maximum wavelength. The reduced form of D2 possesses an
absorption maximum at 580 nm, which corresponds to an intense
blue color. Increasing the degree of oxidation in D2 gradually
decreases the absorbance intensity at 580 nm, and simultaneously,

A. Aydın, I˙ . Kaya / Electrochimica Acta 65 (2012) 104–114
109
Fig. 2. The FT-IR spectra of (a) 3,6-dibromocarbazole, A1 and B1, (b) P(B2), C2 and D2.
shifts this band to longer 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
sub-gap absorption grew at the expense of the ␲–␲* transition
[40]. Fig. 4b shows the changes in the absorption spectra of P(B1),
C1 and D1 at various applied potentials. When different potentials
are applied to P(B1) and C1, their absorbance did not increase;
however, these polymers are easily electropolymerizable (see

1
10
A. Aydın, I˙ . Kaya / Electrochimica Acta 65 (2012) 104–114
Fig. 3. Cyclic voltammograms for repeated scans of (a) P(B2), D2 and C2 as well as (b) P(B1) and C1 (scan rate: 0.25 V/s, cycle numbers: 20 and cycle number for C2: 100).
Figs. 3b and 4b). Increasing the degree of oxidation in D1 gradually
decreases the absorbance intensity at 580 nm, and simultaneously,
shifts this band to longer wavelengths.
spectroscopy method were performed for various scan cycle num-
bers. The potential scan range was different for each polymer. The
results are given in Fig. 5. The measurements were conducted using
a single wavelength with obviously changing absorption intensity.
A scan rate of 0.1 V/s was chosen. During the switching experiment,
the ꢀmax values of 715, 800 and 580 nm were chosen for P(B2),
C2 and D1, respectively. The polymer films were deposited onto
the ITO-coated glass slides under constant potential conditions, as
3.4. Electrochromic switching and the stabilities
To conduct the spectro-electrochemical measurements,
repeated scans with a cyclic voltammeter coupled to an optical

A. Aydın, I˙ . Kaya / Electrochimica Acta 65 (2012) 104–114
111
Fig. 4. Optoelectrochemical spectra of (a) P(B2), C2 and D2 as well as (b) P(B1), C1 and D1 in the presence of 0.1 M LiClO4 in AN.
mentioned above, and their absorbances were monitored at ꢀmax
while switching between potentials. As shown in Fig. 5a, during
the repeated potential scans, the absorption intensity of P(B2) at
found to be 9 s. As shown in Fig. 5b, C2 also had good absorption
recoveries at the applied potentials, which indicates the percent
transmittance (ꢁT%) at 800 nm. The stability of the redox states
during the scans is the most property for an electro-active polymer
to be useful in constructing new electrochromic devices [34,39].
7
15 nm was clearly stable between 0 and 1.6 V. The response times
for P(B2) from the neutral (0 V) to the oxidized (1.6 V) states were

1
12
A. Aydın, I˙ . Kaya / Electrochimica Acta 65 (2012) 104–114
Fig. 5. Electrochromic switching of the optical absorbances of (a) P(B2) at 715 nm, (b) C2 at 800 nm and (c) D1 at 580 nm in the presence of 0.1 M LiClO4 in AN.
The response times for C2 from the neutral (0 V) to the oxidized
1.3 V) states were found to be 13 s at 800 nm. The ability of a
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% transmissive
(%ꢁT = 55%) [41]. Therefore, the transmittances of the polymeric
structures can be low because of the effects from alkyl and etheric
groups.
(
material to exhibit a noteworthy color change is important for
electrochromic applications. The synthesized electrochemical
polymers on ITO-glass exhibited brown colors in the neutral states
and both blue and green colors in the oxidized states. As shown
in Fig. 5c, the response time for D1 from the neutral (−0.4 V)
to the oxidized (1.5 V) states was found to be 13 s. During the
switching process, the percent transmittance (T%) was recorded
using a UV–vis spectrophotometer. The optical contrast (ꢁT%) was
measured as the difference between the T% values recorded for the
neutral and oxidized polymer films and found to be 35% at 715 nm
for P(B2), 33% at 800 nm for C2 and 36% at 580 nm for D1. As a result
of their alkyl – 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
3.5. Thermal stability
The thermal degradation data (TG, DTG and DTA) for the com-
pounds are summarized in Table 1, and the TG curves for the
compounds are shown in Fig. 6. According to the TG results, the
initial degradation temperatures (Ton) of the compounds were less
◦
than 200 C. Weight losses of 20% and 50% were found at 415 and
◦
◦
246 C, respectively, for B1; and 783 and 667 C, respectively, for
B2. The char from B1 and B2 was 20.46% and 10.00%, respectively,
at 1000 C. Additionally, the char values indicated that C2 is ther-
◦
◦
mally unstable, as a 0.00% carbon residue remained at 1000 C. T
max
Table 1
Thermal degradation values of the compounds.
◦
◦
TGA ( C)
DTA ( C)
Tona
Tmaxb
T20c
T50d
% Char at 1000
◦
C
◦
Losses of solvent, % 25–105 C
Exo
Endo
Compounds
B1
B2
D1
D2
C2
186
141
174
174
134
233, 334, 437, 534, 854
157, 367, 661, 814
204, 353, 680, 762
242, 348, 680, 865
180, 301, 570, 788
415
246
228
237
208
783
667
408
356
382
20.46
10.00
18.76
5.00
4.00
–
7.70 365,
5.50
4.50
376, 536
556
–
165, 370
540
359
–
–
–
–
0.00
aThe onset temperature. bTemperature of the peak maxima. cTemperature corresponding to 20% weight loss. dTemperature corresponding to 50% weight loss.

A. Aydın, I˙ . Kaya / Electrochimica Acta 65 (2012) 104–114
113
Fig. 6. TG curves of the synthesized compounds.
Table 2
values were clearly determined from the DTG curve, which indi-
◦
Conductivities of D1, D2, C2, and P(B2).
cated endothermic peaks for B2 at 165 and 370 C. Moreover, there
◦
◦
−1
Conductivity (S cm )
were exothermic peaks at 376 and 536 C for B1; 556 C for B2; 365
Compounds
◦
◦
and 540 C for D1, and 359 C for D2. At the same time, the solvent
removal occurred between 25 and 105 C for a 4.00–7.70% mass
−4
D1
D2
1.8 × 10
◦
3.1 × 10−6
−
−
4
5
loss.
C2
P(B2)
1.5 × 10
5.0 × 10
3.6. Conductivity measurements
3.7. Fluorescence properties
The conductivities of electrochemically prepared polymer films
were measured on the electrode surface via the four-probe tech-
nique at room temperature. When the polymer films coated on
ITO/glass were exposed to iodine vapor, no structural changes from
iodine complexation were observed for the polymers, and their
conductivities were, therefore, stable (see Table 2).
The fluorescence characteristics of the synthesized polymers
were investigated in DMSO because the compounds were com-
pletely soluble in DMSO. These measurements were performed
at two wavelengths for D1 (400 nm and 500 nm) and only one
wavelength for P(B2) (400 nm). Both D1 and P(B2) fluoresced well.
Fig. 7. Fluorescence spectra of (a) D1 and (b) P(B2) (slit width: 5 nm).

1
14
A. Aydın, I˙ . Kaya / Electrochimica Acta 65 (2012) 104–114
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Interestingly, strong green and yellow emissions were obtained
from both DMSO solutions though they were different colors under
daylight, with P(B2) being light yellow under daylight and D1 being
violet. The excitation and emission wavelengths for P(B2) were 295
and 504 nm at 400 nm, whereas the excitation and emission wave-
lengths for D1 were 468 and 525 nm at 400 nm. When the excitation
and emission wavelengths were adjusted to 500 nm, two peaks at
[
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4
56 and 562 nm were obtained with a high intensity. This change
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4
. Conclusions
[
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The synthesized polymers exhibited PL emissions in a DMSO
solution that were tunable to different colors, green and yellow
specifically, by tuning the excitation wavelength. Conductivity
measurements demonstrated that these polymers were semi-
conducting. This result can be explained by the presence of alkyl
and etheric groups in the polymer structures, which decreases
conductivity. Spectroelectrochemical analysis of P(B1) and C1 was
performed at different potentials but no changes in their opti-
cal absorbance was observed; however, these materials were
easily electropolymerizable. Fluorescence analysis demonstrated
that D1 was fluorescent with yellow emission, while P(B2) had
green emission. As a result, these polymers could be used to
produce new green and yellow polymeric light emitting diodes
[
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Acknowledgment
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6
[
The authors thank Government Planning Organization
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