Donor-acceptor type polymers containing the 2,3-bis(2-pyridyl)-5,8-dibromoquinoxaline acceptor and different thiophene donors: Electrochemical, spectroelectrochemistry and electrochromic properties

Article abstract of DOI:10.1039/c5nj02651b

Three donor-acceptor type π-conjugated polymers, poly[2,3-di(2-pyridyl)-5,8-bis(2-thienyl)quinoxaline] (PPTQ), poly[2,3-di(2-pyridyl)-5,8-bis(2-(3-butylthiophen))quinoxaline] (PPBTQ) and poly[2,3-di(2-pyridyl)-5,8-bis(2-(3,4-ethylenedioxythiophene))quinox

Full text of DOI:10.1039/c5nj02651b

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Donor–acceptor type polymers containing the
2,3-bis(2-pyridyl)-5,8-dibromoquinoxaline
Cite this:DOI: 10.1039/c5nj02651b
acceptor and different thiophene donors:
electrochemical, spectroelectrochemistry and
electrochromic properties†
ab
ab
b
b
b
Shuang Chen, Di Zhang, Min Wang, Lingqian Kong and Jinsheng Zhao*
Three donor–acceptor type p-conjugated polymers, poly[2,3-di(2-pyridyl)-5,8-bis(2-thienyl)quinoxaline]
PPTQ), poly[2,3-di(2-pyridyl)-5,8-bis(2-(3-butylthiophen))quinoxaline] (PPBTQ) and poly[2,3-di(2-pyridyl)-5,8-
(
bis(2-(3,4-ethylenedioxythiophene))quinoxaline] (PETQ), containing the 2,3-di(2-pyridyl) quinoxaline moiety in
the backbone as the acceptor unit and different thiophene derivatives as donor units were synthesized
electrochemically. Characterization of the corresponding polymers was conducted by cyclic voltammetry (CV),
UV-vis-NIR spectroscopy and scanning electron microscopy (SEM). Spectroelectrochemistry and
electrochemical analyses demonstrated that all three polymers can undergo both p- and n-type doping
processes. PPTQ exhibits purple red color in the reduced state, violet blue color in the neutral state, and
gray blue color in the oxidation state. PPBTQ exhibits red color in the reduced state, light steel blue color
in the neutral state, and dark slate blue color in the oxidation state. PPETQ exhibits green color in the
reduced state, yellow color in the neutral state, and a colorless highly transmissive state in the oxidation
state. PPETQ and PPBTQ revealed excellent optical contrasts of 80.3% and 78.2%, respectively, in the NIR
region. The outstanding optical contrasts in the NIR region, high stability and fast switching times make
these polymers excellent candidates for NIR device applications.
Received (in Montpellier, France)
2
9th September 2015,
Accepted 22nd December 2015
DOI: 10.1039/c5nj02651b
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importance for the fabrication of EC devices such as smart
windows. The polymers with low band gaps usually produce
Introduction
7
The organic p-conjugated polymers have attracted extensive cathodically coloring materials because of the lower energy
8
attention over time after their discovery since they offer great transition in the doped state. Low band gap donor–acceptor
potential for advanced technological applications, such as polymers are of interest owing to the possibility of attaining
1
electrochromic devices, light emitting diodes and field effect multiple redox states (p-type or n-type doping) in a small
2
–5
transistors.
Electrochromic (EC) polymers are concisely potential window. This is due to the placement of the valence
9
defined as polymers that can reversibly change color by altering band relative to the conduction band. By alternating electron
their redox states. And creating such kinds of electrochromic rich (donor, D) and electron poor (acceptor, A) moieties in the
materials with low band gaps, high optical contrasts, fast response main chain of the D–A type polymers, it is possible to accurately
times, superior coloration efficiencies, low costs and easy processing tune the optical band gap and redox potentials that control the
is always what all the researchers continually seek.
The cathodically coloring polymers (polymers with colored
reduced and transmissive oxidized states), such as polymers with withdrawing imine nitrogens (CQN) are typical acceptor-type
6
10
coverage of optical absorption.
It is well known that aromatic compounds with electron-
1
1,12
neutral green and oxidation transmissive properties, are of great building blocks.
Quinoxaline derivatives like these kinds of
organic molecules combined in the D–A type polymers as the
acceptor moiety have attracted increasing interest in recent
years. Besides, the quinoxaline-fused ring can ensure a rigid
coplanar backbone and a highly extended p-electron system
with strong p-stacking, which are crucial requirements for the
high-performance electrochromic materials. Additionally, different
a
b
Department of Chemical Engineering, China University of Petroleum (East China),
QingDao, 266580, P. R. China
Shandong Key Laboratory of Chemical Energy Storage and Novel Cell Technology,
Liaocheng University, Liaocheng, 252059, P. R. China. E-mail: j.s.zhao@163.com;
Fax: +86-635-8539607; Tel: +86-635-8539607
1
3
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nj02651b thiophene-based derivatives such as a series of donor moieties
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have gained much attention during the past decades, owing to Experimental
the variation of the optical and electronic properties by light
Materials
14,15
structural modification.
Therefore the combination of different
3
3
,4-Ethylenedioxythiophene (EDOT) (99%), thiophene (99%),
-butylthiophene (99%), and dibromo-2,1,3-benzothiadiazole
thiophene derivatives and quinoxaline compounds is considered as
a promising way to obtain new polymers with excellent electro-
1
6
(98%) were all purchased from Puyang Huicheng Electronic
Material Co., Ltd and used as received. p-Toluenesulfonic acid
chemical properties. Poly(2,3-bis(3,4-bis(decyloxy)phenyl)-5,8-
bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)quinoxaline) (PDOPEQ)
as an example of quinoxaline based polymer revealed processable
green-to-transmissive electrochromism with superior optical
contrasts and fast switching times, which make this polymer
(PTSA, 98%), sodium borohydride (NaBH
4
, 98%), bis(triphenyl-
Cl ), anhydrous ethyl
phosphine)dichloropalladium (Pd(PPh
3
)
2
2
0
alcohol (EtOH, 99.9%), 2,2 -pyridyl (98%), n-butyllithium (2.5 M)
and chlorotributyltin (97%) were all purchased from Aladdin
Chemical Co., Ltd China. Commercial high-performance liquid
chromatography grade acetonitrile (ACN, Tedia Company, INC.,
USA) and dichloromethane (DCM, Sinopharm Chemical Reagent
Co., Ltd, China) were used as received without further purification.
17
unique among numerous electrochromic conjugated polymers.
The synthesis of conjugated polymers with various optical band
gaps and color changes is a major driving force for the development
18
of electrochromic materials. During the course of preparing the
D–A type electrochromic materials, the change in the structure type
of the acceptor unit with the same donor unit can effectively tune
the electrochromic properties of the polymers, including the optical
Tetra-n-butylammonium hexafluorophosphate (TBAPF
6
, Alfa Aesar,
98%) was dried in vacuum at 60 1C for 24 hours before use.
1
9
Tetrahydrofuran (THF, Tianjin Windship Chemistry Technological
Co., Ltd, China) was distilled over Na in the presence of
benzophenone prior to use. Indium-tin-oxide-coated (ITO) glass
band gaps and the color changes. Recently, a new conjugated
polymer with donor–acceptor architectures based on alternating
1,4-divinyl-2,5-dioctyloxybenzene and 5,8-(2,3-dipyridyl)-quinoxaline
ꢀ
1
(
sheet resistance: o10 O & , purchased from Shenzhen CSG
units was synthesized and characterized with respect to its
properties as polymer solar cell materials and trinitrotoluene
Display Technologies, China) was washed with ethanol, acetone
and deionized water successively under ultrasonication, and
2
0
sensing materials. However, to the best of our knowledge,
there are no reports concerning the synthesis and characterization
of the D–A type polymers containing the alternating 5,8-(2,3-
dipyridyl)-quinoxaline units and the bithiophene units, although
these types of conjugated polymers usually have excellent electro-
chromic properties including fast switching times, outstanding
stabilities, and high contrast ratios in the visible and near infrared
regions.
2
then dried under N flow.
Synthesis procedure
,6-Dibromo-1,2-phenylenediamine and 2,3-bis(2-pyridyl)-
3
5,8-dibromoquinoxaline. 5.75 g (19.56 mmol) of 4,7-dibromo-
2,1,3-benzothiadiazole and 250 mL of anhydrous ethyl alcohol
were added into a round-bottom flask, meanwhile, 16.5 g
(
436 mmol) of NaBH
4
was added in three installments gradually
Based on the above consideration, three novel monomers
including 2,3-di(2-pyridyl)-5,8-bis(2-thienyl)quinoxaline (PTQ),
(at 0 h, 8 h and 16 h, respectively). The solution was stirred in
an ice bath at 0 1C for 48 h. After the reaction, the mixture was
2
,3-di(2-pyridyl)-5,8-bis(3-butylthiophen-2-yl)quinoxaline (PBTQ)
and 2,3-di(2-pyridyl)-5,8-bis(2-(3,4-ethylenedioxythienyl))quinoxaline
PETQ) were synthesized by Stille coupling reaction in advance.
poured into distilled water, stirred and filtered to obtain a white
2
1 1
3
(
,6-dibromo-1,2-phenylenediamine solid (3.38 g, 65%). H-NMR
(
13
400 MHz, CDCl ; d/ppm): 6.75 (s, 2H), 3.83 (s, 4H). C-NMR
And then, the monomers were electrochemically synthesized to
their corresponding polymers including PPTQ, PPBTQ and
PPETQ. The electrochemical and electrochromic properties
of these polymers were also described. It was interesting to find
that the slight structural change in three polymers could give rise
to a significant difference in electrochemical and color change.
Through the analysis of the data results, the strong ethylenedioxy-
thiophene electron-donating group can successfully tailor the
electrochromic properties by combining a low monomer oxidation
potential and a narrow band gap as well as high electrical
conductivity. In addition, PPETQ showed a green color in
the reduced state, a deep yellow color in the neutral state
and a highly transmissive oxidized state, which are not yet
reported so far.
3
(
100 MHz, CDCl ; d/ppm): 133.74, 123.37, 109.70.
3
A solution of 2,3-diamino-1,4-dibromobenzene (1.03 g, 3.8 mmol),
0
2
,2 -bipyridyl (0.806 g, 3.8 mmol) and 6 mL of acetic acid in 25 mL of
ethanol was heated to reflux for 3 h, then cooled to 0 1C. The formed
precipitate was isolated by filtration and washed with ethanol to
2
0
afford 1.16 g of 2,3-diamino-1,4-dibromobenzene as a yellow solid.
1
Yield 70%, mp: 251–253 1C. H NMR (CDCl ; d/ppm): 7.25–7.28 (d,
H), 7.87–7.98 (d, 6H), 8.26–8.32 (m, 2H). C NMR (CDCl ; d/ppm):
3
13
2
3
1
23.4, 123.8, 125.4, 133.6, 136.9, 148.2, 153.4, 156.5. Anal. calcd (%)
for C18 (442.11): C, 48.90; H, 2.28; N, 12.67. Found (%): C,
8.01; H, 2.47; N, 11.53.
H10Br N
2 4
4
PTQ, PBTQ and PETQ
All three polymers exhibited high optical contrasts, reasonable As shown in Scheme 1, PTQ, PBTQ and PETQ were synthesized
coloration efficiencies (CE) and satisfactory response times. What via Stille cross coupling reaction. Tributylstannane compounds
1
7
is more, the presentation of redox peaks and variation of the were prepared according to previous literature methods. 2,3-
spectroelectrochemistry at negative potentials prove the real Bis(2-pyridyl)-5,8-dibromoquinoxaline (1.768 g, 4 mmol) and
existence of an n-doping process for all three polymers. These the excessive corresponding tributylstannane compounds (16 mmol)
characteristics make the polymers candidates for important were dissolved in dry THF (60 mL). Pd(PPh
3 2 2
) Cl (0.28 g, 0.4 mmol)
application prospects in the field of smart electrochromism. used as the catalyst was also added in the solution. The solution was
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1
3
7
1
1
6
3
.94 (t, 2H, ArH), 6.57 (s, 2H), 4.36 (dd, 8H). C NMR (CDCl ,
01 MHz, ppm): d = 157.54, 150.31, 148.23, 141.58, 140.62,
37.15, 136.96, 129.09, 128.78, 124.97, 123.03, 113.43, 103.37,
5.15, 64.53 (see ESI,† Fig. S3). Anal. calcd (%) for C H N S :
3
4
32 4 2
C, 72.82; H, 5.75; N, 9.99; S, 11.44. Found: C, 72.77; H, 5.87;
+
N, 9.89; S, 11.49. mp, 135.2 1C. HRMS (m/z, EI ) calcd for
C
34
H
32
N
4
S
2
, 560.77, found 560.89.
Instrumentation
1
13
H NMR and C NMR spectra of the monomers were recorded
on a Varian AMX 400 spectrometer in CDCl at 400 MHz and
3
chemical shifts (d) were given relative to tetramethylsilane used
as the internal standard Scanning electron microscopy (SEM)
measurements were taken by using a Hitachi SU-70 thermionic
field emission SEM. UV-vis-NIR spectra were carried out on a
Varian Cary 5000 spectrophotometer under the control of a
computer. Digital photographs of the polymer films were taken
using a Canon Power Shot A3000 IS digital camera. Electrochemical
syntheses and experiments were performed in a one-compartment
cell using a CHI 760 C electrochemical analyzer (Shanghai Chenhua
Instrument Co. China) under control of a computer. Elemental
analyses are performed on a Thermo Finnigan Flash EA 1112,
Scheme 1 Synthetic route of the monomers.
stirred in a nitrogen atmosphere for 30 min at room temperature CHNS-O elemental analyses instrument. The thickness and
increasing the temperature immediately until the solution was surface roughness of the polymer films were recorded on a
refluxed. The mixture was refluxed for 24 h, and then concentrated KLA-Tencor D-100 step profiler. Mass spectrometry analysis was
on a rotary evaporator. The reaction mixture for the PTQ monomer conducted using a Bruker maXis UHR-TOF mass spectrometer.
was purified using column chromatography on silica gel, in which
Electrochemistry
n-hexane–dichloromethane (2 : 1 by volume) was the eluent. The
1
purified product PTQ is a yellow solid. H NMR (CDCl
3
, 400 MHz, Electrochemical syntheses and experiments were performed in
ppm): d = 8.46 (d, 2H, ArH), 8.30 (d, 2H, ArH), 8.20 (s, 2H, ArH), a one-compartment cell using a CHI 760 C Electrochemical
.96 (t, 2H, ArH), 7.88 (d, 2H,), 7.55 (d, 2H), 7.26(t, 2ArH), 7.21(t, Analyzer (Shanghai Chenhua Instrument Co. China) under
7
2
13
H). C NMR (CDCl
43.08, 138.92, 137.36, 136.94, 131.781, 129.03, 127.85, 126.89, was a platinum wire with a diameter of 0.5 mm, a platinum ring
24.79, 123.20 (see ESI,† Fig. S1). Anal. calcd (%) for C26 : C, served as a counter-electrode, and a silver wire (Ag wire) was
9.62; H, 3.60; N, 12.48; S, 14.30. Found: C, 69.57; H, 3.59; N, 12.53; employed as a pseudo reference electrode. The working and
3
, 101 MHz, ppm): d = 157.65, 151.39, 148.31, control of a computer at room temperature. The working electrode
1
1
16 4 2
H N S
6
+
S, 14.31. mp, 176.5 1C. HRMS (m/z, EI ) calcd for C H N S , counter-electrodes for cyclic voltammetric experiments were
26 16 4 2
4
48.56, found 448.23.
The reaction mixture for the PBTQ monomer was purified polymerization and CV tests were performed in DCM containing
using column chromatography on silica gel, in which n-hexane– 0.1 M TBAPF as a supporting electrolyte with or without 4 mM
dichloromethane (3 : 1 by volume) was the eluent. The purified monomers. The pseudo reference electrode was calibrated
placed 0.5 cm apart during the experiments. All electrochemical
6
1
+
product PBTQ is an orange yellow solid. H NMR (CDCl
3
,
externally using a 5 mM solution of ferrocene (Fc/Fc ) in DCM
as the electrolyte, and the
400 MHz, ppm): d = 8.46 (d, 2H, ArH), 8.29 (d, 2H, ArH), 8.14 solution containing 0.1 M TBAPF
6
+
(s, 2H, ArH), 7.94 (t, 2H, ArH), 7.72 (d, 2H,), 7.25 (t, 2H, ArH), half-wave potential (E1/2) of Fc/Fc measured was 0.39 V vs. Ag
+
7
.1(d, 2H), 2.7 (t, 4H), 1.7 (m, 4H),1.44 (m, 4H), 0.97 (t, 6H). wire. Concerning the fact that the E1/2 of Fc/Fc measured in
1
3
3
6
C NMR (CDCl , 101 MHz, ppm): d = 157.64, 151.12, 148.32, DCM solution containing 0.1 M TBAPF was 0.42 V vs. SCE, the
1
0
1
1
43.06, 138.50, 137.35, 137.05, 131.65, 128.46, 127.69, 124.83, potential of Ag wire was assumed to be 0.03 V vs. SCE. All of
24.15, 123.22, 33.01, 30.48, 22.69, 14.25 (see ESI,† Fig. S2). the electrochemical experiments were carried out at room
Anal. calcd (%) for C30
H
20
N
4
O
4
S
2
: C, 63.81; H, 3.57; N, 9.92; O, temperature in a nitrogen atmosphere, and using the Ag wire
1
1
5
1.33; S, 11.36. Found: C, 63.49; H, 3.89; N, 9.43; O, 11.67; S, as the pseudo reference electrode. Cyclic voltammetry (CV) of
+
1.52. Mp, 309.8 1C. HRMS (m/z, EI ) calcd for C30
H
20
N
4
O
4
S
2
,
the polymer was carried out using the same electrode set-up in
monomer-free electrolyte solution.
64.63, found 564.56.
The reaction mixture for the PETQ monomer was purified
using column chromatography on silica gel, in which n-hexane–
Spectroelectrochemistry
dichloromethane (3 : 1 by volume) was the eluent. The purified Spectroelectrochemical data were recorded on a Varian Cary
1
product PETQ is a red solid. H NMR (CDCl
3
, 400 MHz, ppm): 5000 spectrophotometer connected to a computer. A three-
d = 8.67 (s, 2H, ArH), 8.48 (d, 2H, ArH), 8.28 (d, 2H, ArH), electrode cell assembly was used where the working electrode
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2
was an ITO glass with a surface area of 0.9 ꢁ 1.8 cm , the present a weak oxidation peak at 0.78 V and a reduction peak at
counter-electrode was a stainless steel wire, and an Ag wire was 0.38 V (Fig. S4b, ESI†). In addition, the increase in the redox
used as a pseudo reference electrode. The thickness of the wave current densities implies that the amount of conducting
22
polymer films grown potentiostatically on ITO was controlled polymers deposited on the electrode is increasing. The electro-
by the total charge passed through the cell. The measurements chemical polymerization reaction is an electrophilic substitution
were carried out in DCM solution containing 0.1 M TBAPF
Color changes were recorded with in situ electrocolorimetric cation intermediate. Taking the polymerization of PTQ as an
6
.
which retains the aromatic structure and proceeds via a radical
23
measurements under potentiostatic control using a Varian Cary example, its polymerization mechanism by the electrochemical
5000 spectrophotometer in color measurement mode. The standard method is shown in Fig. S5 (ESI†).
illuminant D65 with a 21 observer at constant temperature in a light Electrochemical behavior of the polymer films. In order to
booth designed to exclude external light was used. Prior to each set make research on the electrochemical properties, three polymer
of measurements, background color coordinates (x, y and z values) films were prepared on a Pt wire by sweeping the potentials for
were taken at open-circuit, using the electrolyte solution without the three cycles. Electrochemical behaviors of the deposited polymers
ꢀ1
polymer films under the study.
were investigated at different scan rates between 100 and 300 mV s
in monomer free electrolyte solution, as shown in Fig. 2. Fig. 2a
shows the electrochemical behavior of the PPETQ film at different
Results and discussion
ꢀ1
scan rates from 300 to 50 mV s in DCM containing 0.1 M TBAPF
6
.
Electrochemical polymerization and characterization
The polymer film exhibits a redox process between 0.42 and 0.5 V
p-doping). A couple of redox peaks with an oxidation potential of
(
Electrochemical polymerization. All the polymers were poly-
ꢀ
1.26 V and a reduction potential of ꢀ1.4 V are also observed in the
merized on the platinum wire by cyclic voltammetry (CV) at the
ꢀ1
reduction region, which indicates that the polymer can be n-doped.
What is more, the redox peaks of n-doping/dedoping are much
stronger than the p-doping/dedoping process. The results suggest
that 2,3-bis(2-pyridyl)-5,8-dibromoquinoxaline is a strong electron
same potential scan rate (100 mV s ). The successive CV curves
of 4 mM PTQ, PBTQ and PETQ in 0.1 M TBAPF /DCM electro-
6
lyte are illustrated in Fig. 1. Among them, the first cycle of CV
test is ascribed to the oxidation of monomers. The onset
oxidation potentials (Eonset) of PTQ and PBTQ are 1.08 and
24
acceptor and PPETQ is a good n-type conjugated polymer. This
phenomenon is also observed in other polymers including PPTQ
and PPBTQ (see ESI,† Fig. S6b and S7b) although there are no
obvious n-dedoping peaks in both of the polymers. The different
locations and different appearances of the oxidation and reduction
peaks of the polymers reveal the influence of different electron-rich
groups. Fig. 2b and c shows good linear relationships between the
scan rate and peak current densities ( j) of the PPETQ polymer
during the p-doping/dedoping process and the n-doping/dedoping
process, which demonstrate that the films well adhered to ITO and
1.06 V, respectively, with the latter slightly lower than that of
the former, the reason for which might be the weak electron
donating ability of the butyl group on the thiophene ring. By
comparison, the Eonset of PETQ is 0.83 V, being far lower than
that of PTQ and PBTQ, due to the presence of a strong electron
donating group on the donor moiety. During the successive
anodic scan of the monomer, the corresponding polymer films
were formed on the surface of the working electrode. As shown
in Fig. 1, the CV curves of PPTQ show a cathodic peak at around
25
the electrochemical processes are non-diffusion-controlled. The
other two polymers including PPTQ and PPBTQ also present similar
linear relationships between the scan rates and the peak current
densities (Fig. S6a and S7a, ESI†).
0.93 V, while the corresponding oxidation waves are overlapped
with the oxidation waves of the monomer and cannot be
observed clearly. Similarly, the CV curves of PBTQ show only
a cathodic peak at around 1.0 V with the corresponding oxidation
waves overlapped (Fig. S4a, ESI†). However, the CV curves of PETQ
Meanwhile, the PETQ monomer is also found to exhibit a
true n-doping behavior (Fig. S8, ESI†). The cyclic voltammogram
of the PETQ monomer was recorded between ꢀ1.7 V and +1.2 V
ꢀ
1
6
at a scan rate of 100 mV s in 0.1 M TBAPF /DCM solution, and
the sweep was started from an initial potential of 0 V, and then a
positive scan which was followed by a negative scan. The PETQ
exhibits an oxidation peak (or p-doping) at 0.95 V and a reduction
peak (or n-doping) at ꢀ1.55 V, and the corresponding p-dedoping
and n-dedoping peaks were coupled at 0.59 V and ꢀ1.31 V,
respectively. These results also support the structure of the
monomer having both the strong electron-donating 3,4-ethylene-
dioxythiophene unit and the electron-accepting quinoxaline unit.
Morphology
Scanning electron micrographs (SEM) of polymers provide their
clear surface and bulk morphologies, which are closely related
to their optical and electrical properties. Fig. 3 shows the SEM
images of PPTQ, PPBTQ and PPETQ, which were prepared
6
Fig. 1 Cyclic voltammogram curves of PTQ in 0.1 M TBAPF /DCM solution
2
6
ꢀ1
at a scan rate of 100 mV s . j denotes the current density. E denotes
the potential.
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globular cluster structure with scattered holes between the
clusters. A cauliflower structure is observed on the surface of
the PPBTQ film (Fig. 3b). However, PPETQ reveals a coral
structure with dense holes between the globules (Fig. 3c). A
step profiler was employed for evaluating the thickness and
roughness of three polymer films deposited on the ITO electrode
ꢀ2
with a polymerization charge of 2.0 ꢁ 10 C at a surface area of
2
0
.9 ꢁ 1.8 cm . The thickness profiles of three polymer films are
shown in Fig. S9 (ESI†), and the thicknesses were measured to be
27 nm, 896 nm and 625 nm for PPTQ, PPBTQ and PPETQ,
8
respectively. The profiles of the step profiler measurements
revealed that the polymer films have extremely rough surfaces with
detectable pits, which is in good agreement with the morphologies
shown in the SEM images. The morphologies of the three polymers
Fig. 2 (a) CV curves of PPETQ at different scan rates between 50 and
ꢀ1
3
00 mV s in the monomer-free 0.1 M TBAPF /DCM solution. (b) Scan
6
rate dependence of the anodic and cathodic peak current densities graph
of the p-doping/dedoping process. (c) Scan rate dependence of the
anodic and cathodic peak current densities graph of the n-doping/dedoping
process. jp.a and jp.c denote the anodic and cathodic peak current densities,
respectively.
potentiostatically in the solution of 0.1 M TBAPF /DCM containing
6
relevant monomers on ITO electrodes and dedoped before
characterization. It is clearly observed that the three polymers
exhibit different surface morphologies, even though their structures
Fig. 3 SEM images of (a) PPTQ, (b) PPBTQ and (c) PPETQ films deposited
are quite similar. As shown in Fig. 3a, the PPTQ film exhibits a potentiostatically on an ITO electrode.
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were quite different from each other, which might be an indication the near infrared region centered at 810 nm. It is apparent that
of the different aggregate structures of the conjugated polymers, three polymers exhibit a certain amount of red-shift compared
and also accounting for the different film thicknesses although the to the corresponding monomers as shown in Fig. 4, which
polymers had the same polymerization charges.
indicate the formation of the long conjugated polymer chains
due to the fact that the longer the wavelength of maximum
absorption is, the higher the conjugation length in the polymer
Optical properties of the monomers and films
2
7
As the typical feature of D–A conjugated compounds, all three will be. Besides, the optical band gaps (E
g
) of the three
monomers exhibit two characteristic absorption bands, which polymers were calculated from its low energy absorption edges
are assigned to the strong p–p* transition and intramolecular (lonset) (E
charge transfer, respectively. Two obvious absorption peaks easily seen that the prepared polymer film of PPETQ has a lower
g
= 1240/lonset). Based on previous results, it can be
8
can be observed at about 310 and 448 nm for PTQ, 313 and band gap than that of PPTQ and PPBTQ. The E
45 nm for PBTQ, and 323 and 471 nm for PETQ, respectively. was calculated to be 1.16 eV, which was lower than that of
of the PPETQ
g
4
Compared with PTQ and PBTQ, PETQ has an apparent red shift PPBTQ (1.74 eV) and PPTQ (1.54 eV). The weak electron donating
of the maximum absorption wavelengths due to the electron effect of the butyl group on the thiophene ring cannot compensate
donating ability of the electron rich ethylenedioxy group, which for its repulsive steric effect on the neighboring repeat unit that
8
enhances the conjugation effect of the D–A compound effectively. decreases the effective conjugation length of the homopolymers.
Similarly, there is a little red-shift of the maximum absorption This explained the fact that PPBTQ has a slightly larger band gap
wavelengths of PBTQ compared with that of PTQ due to the weak than that of PPTQ.
electron donating effect of the butyl group on the thiophene
Table 1 summarizes the onset oxidation potential (Eonset),
moiety. Furthermore, the frontier molecular orbitals of the maximum absorption wavelength (lmax), low energy absorption
monomers were investigated by using density functional theory edges (lonset), HOMO and LUMO energy levels, and optical
(
g
DFT) with the Gaussian 03 program at the parameters of B3LYP band gap (E ) values of the monomers and the corresponding
and 6-31+G* basis sets. The ground-state electron density polymers, as well as the calculated band gap data for the
distribution of the highest occupied orbital (HOMO) and the monomers from the Gaussian 03 program. Their HOMO energy
lowest unoccupied molecular orbital (LUMO) are illustrated in levels were calculated by using the formula EHOMO = ꢀe(Eonset + 4.4)
Fig. S10 (ESI†). The LUMOs are more localized on the electron- (vs. SCE) and their LUMO energy levels (ELUMO) were calculated by
28
accepting quinoxaline moiety, while HOMOs are delocalized on subtracting the optical band gap (E ) from the HOMO levels.
g
the electron-donating thiophene moieties, respectively. And, the
results of DFT calculation also confirmed the electron transfer
between the donor unit and the acceptor unit, which accounted
Electrochromic properties of the polymer films
Spectroelectrochemical properties of the polymers. Spectro-
for the low band gaps of the D–A–D type monomers.The electrochemistry is a useful method for studying the optical
calculated HOMO–LUMO gaps of the monomers were found changes in the absorption spectra and gain information about
to be in the range of ꢀ2.75 eV to ꢀ2.94 eV and the data are the electronic structures of conjugated polymers as a function
2
9
summarized in Table 1. The highest band gap was observed for of the applied potential difference. Three polymer film coated
PTQ and the lowest for PETQ, which is consistent with their ITO electrodes (with the same polymerization charge of 2.0 ꢁ
ꢀ2
strength of the electron donating abilities. UV-vis absorption 10
C at 1.2 V for PETQ and 1.4 V for PTQ and PBTQ,
spectra of three polymer films including PPTQ, PPBTQ and respectively) were switched at different potentials using a UV-vis-
PPETQ on an ITO coated slide glass are shown in the inset of NIR spectrophotometer in monomer-free 0.1 M TBAPF /DCM
Fig. 4. As seen from Fig. 4, both PPTQ and PPBTQ show one solution in order to obtain the in situ UV-vis-NIR spectra (Fig. 5).
absorption band in the visible region due to the p–p* transition The electrochromic behavior was investigated using an
in the neutral state, with the absorption peaks at 610 and UV-vis-NIR spectrometer at various applied potentials (vs.
66 nm, respectively. Different from that of PPTQ and PPBTQ, pseudo Ag wire reference electrode), the absorption changes
6
5
the PPETQ film exhibits two separated absorption bands, with in response are shown due to the localization of the redox
one in the visible region centered at 454 nm, and the other in process. And, for giving an accurate description of the color,
Table 1 The onset oxidation potential (Eonset), maximum absorption wavelength (lmax), absorption onset wavelength (lonset), HOMO and LUMO energy
levels, optical band gap (E ) and the calculated band gap data for the monomers from the Gaussian 03 program
g
a
b
c
d
d
d
Compounds
Eonset, vs. SCE (V)
lonset (nm)
E
g
(eV)
HOMO (eV)
LUMO (eV)
DE
HOMO (eV)
LUMO (eV)
PTQ
1.11
1.09
0.86
0.92
1.04
0.11
515
521
552
807
805
2.41
2.38
2.25
1.54
1.74
1.16
ꢀ5.51
ꢀ5.49
ꢀ5.26
ꢀ5.32
ꢀ5.44
ꢀ4.51
ꢀ10
ꢀ2.94
ꢀ2.79
ꢀ2.75
—
—
—
ꢀ5.50
ꢀ5.31
ꢀ5.12
—
—
—
ꢀ2.56
ꢀ2.52
ꢀ2.37
—
—
—
PBTQ
PETQ
PPTQ
PPBTQ
PPETQ
ꢀ3.11
ꢀ3.01
ꢀ3.78
ꢀ3.70
ꢀ3.35
1069
a
b
c
Calculated from the low energy absorption edges (lonset), E
g
= 1240/lonset
.
HOMO = ꢀe(Eonset + 4.4)(Eonset vs. SCE). Calculated by the
d
subtraction of the optical band gap from the HOMO level. Calculated by employing the Gaussian 03 program.
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Fig. 4 UV-vis spectra of PTQ, PBTQ and PETQ in DCM. Inset: absorption
spectra of the corresponding polymers deposited on ITO in the neutral
state.
the CIE 1931 xy chromaticity co-ordinates were also calculated
from the in situ spectra of each film. All three polymers display
similar absorption in the reduced state, with two distinct
absorption bands. The high-energy peaks of PPTQ mainly
absorb in the UV-region, with minor tailing into the visible
region, limiting the contribution of the high-energy peak to the
color perceived by the human eye (Fig. 5a). On the other hand,
the low-energy peaks, originating from the D–A interaction,
have pronounced absorption in the red part of the visible
region. A broader peak appeared centered at 608 nm due to
p–p* transition, partly absorbing the yellow-brown light,
resulted in a violet blue color for PPTQ (Fig. 6a) in the neutral
state. The electronic band gap of the polymer, defined as the
onset of p–p* transition, was determined to be 1.54 eV. During
oxidation, the p–p* transition bands started to decrease and a
concomitant increase was observed at 755 nm and 1230 nm due
to the formation of charge carriers including polarons and
bipolarons (Fig. 5a). The phenomenon of simultaneous formation
of polarons and bipolarons could be attributed to the presence of
stable bipolaronic states on the polymer backbone during the
doping process. In the fully oxidized state, PPTQ presented a
blue-gray color due to the broad absorption centered at 755 nm,
which partly absorbs the brown and red light (Fig. 5a and 6a).
There are usually two transitions for the neutral states of D–A
type polymers, with one being related to the transition from the
Fig. 5 [a] p-Doping: spectroelectrochemistry of the PPTQ film on an ITO
electrode in the monomer-free 0.1 M TBAPF
potentials: (a) 0.2, (b) 0.8, (c) 0.9, (d) 0.95, (e) 1.0, (f) 1.05, (g) 1.1, (h) 1.15, (i)
thiophene-based valence band to its antibonding counterpart 1.2, and (j) 1.3 V. n-Doping: a bold black line marked by ‘x’ indicates the
6
/DCM solution at applied
reduction spectrum of the PPTQ film at ꢀ1.7 V. [b] p-Doping: spectro-
(
high-energy transition), and the other being related to the
electrochemistry of the PPBTQ film on an ITO electrode in the monomer-free
transition from the thiophene-based valence band to the acceptor
localized conduction band (low-energy transition). In this sense,
the interactions between donor and acceptor units (their match)
0
.1 M TBAPF
.90, (e) 0.925, (f) 0.95, (g) 0.975, (h) 1.0, (i) 1.05, (j) 1.1, and (k) 1.2 V. n-Doping: a
bold black line marked by ‘x’ indicates the reduction spectrum of the PPBTQ
6
/DCM solution at applied potentials: (a) 0.2, (b) 0.8, (c) 0.85, (d)
0
determine the energy and intensity of these transitions. For film at ꢀ1.5 V. [c]. p-Doping: spectroelectrochemistry of the PPETQ film on an
ITO electrode in the monomer-free 0.1 M TBAPF
potentials: (a) ꢀ0.2, (b) 0.2, (c) 0.25, (d) 0.30, (e) 0.35, (f) 0.40, (g) 0.45, (h) 0.5,
i) 0.55, (j) 0.60, (k) 0.65, (l) 0.7 V, (m) 0.80, (n) 0.90, (o) 1.0 V, (p) 1.1, and (q) 1.2 V.
6
/DCM solution at applied
PPTQ, the intensity of the low energy transition was significantly
smaller than that of the high energy transition, which was not
centered in the visible region (with a maximum at 318 nm and
not shown completely in Fig. 5a). The lower intensity of the low-
energy transition might be an indication of the weak inter-
actions or the unsatisfactory match between thiophene and the
(
n-Doping: a bold black line marked by ‘x’ indicates the reduction spectrum of
the PPETQ film at ꢀ1.4 V.
5
,8-(2,3-dipyridyl)-quinoxaline acceptor unit due to the weak
Spectroelectrochemistry of PPBTQ shows a lmax of 566 nm in
the visible region due to the p–p* transition in the neutral state,
electron donating ability of the thiophene unit.
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development of new transition bands at lower energy (at
around 798 nm and 1364 nm, respectively), corresponding to
3
0
the polaronic and bipolaronic charge carriers. The fully
oxidized PPBTQ polymer presents a blue purple color due to
the presence of a significant amount of tails of the polaronic
and bipolaronic absorption bands with a medium maxima
centered at 797 nm due to the formation of the polarons
(
Fig. 5b and 6b). The electronic band gap of the polymer,
defined as the onset of p–p* transition, was determined to be
.74 eV. The different structures of the polymers due to the
1
difference in the donor moiety affect not only the monomer
oxidation and the polymer redox couple potentials but also the
maximum absorption wavelengths of the corresponding transi-
tions. The introduction of an alkyl substituent on the polymer
causes steric hindrance, resulting in less order and less con-
jugation by the blue shift in the absorption spectra and the
8
increase in the polymer band gap. Being similar to PPTQ, there
is also a minor low-energy transition obsorption for PPBTQ,
which might be attributable to the weak interaction between the
acceptor unit and the 3-butylthiophene unit.
Spectroelectrochemical studies of PPETQ reveal two well-
separated absorption maxima centered at 448 and 808 nm,
respectively, with a broad valley centered at 597 nm, which
gives rise to a dark yellow color in the neutral state (Fig. 5c and
6c). Compared with PPTQ and PPBTQ polymers, there are
significant bathochromic shifts for both of the p–p* transition
bands of PPETQ, and the intensities of two transitions are
comparable with each other, which indicates the ideal match
between the donor and acceptor units and the strong interactions
between them. As expected, the band gap of PPETQ calculated
from the onset of p–p* transition is 1.16 eV, which is much lower
than that of the PPTQ and PPBTQ polymers. As has been known,
the hybridization between the highest state of the HOMO level of
the donor with the lowest state of the LUMO level of the acceptor
results in a polymer which has an ionization potential closer to the
31
donor and an electron affinity closer to the acceptor. In this case,
the higher HOMO level of the EDOT unit compared to that of
thiophene and 3-butylthiophene units is the reason for the lowest
band gap of PPETQ among three polymers. The intensities of both
absorption bands decrease and a new absorption band centered at
1430 nm in the NIR region appears due to the formation of charge
carriers upon oxidation of the PPETQ polymer (Fig. 5c). In the full
oxidation state, the loss of absorption in the visible region for the
oxidized state of PPETQ is not complete and residual long
wavelength absorption also remains, giving the highly transmissive
polymer a slight gray hue (Fig. 5c and 6c). As mentioned previously,
the necessity for a cathodically colouring yellow to transmissive
electrochrome is paramount in completing the colour palette for
non-emissive displays using the subtractive colour mixing theories
of CMY (cyan, magenta and yellow) and RYB (red, yellow and blue).
In addition, the conducting polymers with stable negatively
doped states are of high interest. The n-doping of a conjugated
polymer in an n-type manner is not just an electrochemical
formation of a reduced state, which is also accompanied by the
Fig. 6 Calculated colour trajectory in the CIE 1931 colour space for (A)
PPTQ (a, ꢀ1.4 V; b, 0 V; c, 1.4 V), (B) PPBTQ (a, ꢀ1.5 V; b, 0 V; c, 1.4 V), and
(
C) PPETQ (a, ꢀ1.4 V; b, ꢀ0.2 V; c, 1.2 V) films deposited onto ITO/glass.
which is light steel blue in color (Fig. 5b and 6b). Upon introduction of charge carriers. The optical change that occurs
oxidation there is a decrease in the p–p* transition and the during the n-doping of the polymer was examined to prove the
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introduction of a charge carrier to the conjugated system. The Fig. 7a shows the switching properties of PPTQ between 0.2 and
reductive absorption spectra of PPTQ, PPBTQ and PMFTQ are 1.4 V at 1230 nm in NIR regions. The optical contrast for PPTQ was
recorded at ꢀ1.4, ꢀ1.5 and ꢀ1.4 V, respectively, which are the calculated to be 22.8% and the switching times were 4.35 s from
cathodic potentials of the redox couples observed in the the reduced to oxidized state and 3.59 s from the oxidized to
reduced states. For PPTQ, the absorption maxima centered at reduced state at 1230 nm. The stability of PPTQ was not very
5
10 nm in the visible region brought about a purple color, preferable since there was a moderate loss in the percent
which indicates a significant difference from that of the neutral transmittance contrast value after regular switching for 300 s.
and p-doped states (Fig. 5a and 6a). As for PPBTQ, a well- The PPBTQ film was switched from 0.2 V to 1.3 V at 5 s step
defined absorption band centered at 497 nm was found, which intervals while the changes in transmittance were recorded at
resulted in a red reduced state (Fig. 5b and 6b). When ꢀ1.4 V two different wavelengths in both ultraviolet and NIR regions.
was applied for the polymer PMFTQ, the film turned into a The optical contrasts for PPBTQ were calculated to be 16.9% at
valuable green color with two separated absorption waves at 336 nm and 78.2% at 1340 nm (Fig. 7b). PPBTQ had switching
443 and 779 nm, respectively, (Fig. 5c and 6c). The electro-
chemical properties of the reduced states and the spectral
changes that occur upon reduction proved that the n-doping
process truly occurred.
To further establish the colors of the polymers, the colori-
metric properties were characterized using CIEAB 1976 color
space (L*a*b*). L* can be interpreted as being the lightness
variable of the material, while a* and b* are concerned with the
red-green and yellow-blue saturation of the colour, respectively.
The values of the relative L*a*b* were measured in the neutral,
oxidized and reduced states of the polymers and summarized
in Table 2.
Electrochromic switching of PPTQ, PPBTQ and PPETQ films
in solution. It is important that polymers can switch rapidly
and exhibit a noteworthy color change for electrochromic
3
2
applications. For this purpose, double potential step chrono-
amperometry technique was used to investigate the switching
ability of the three polymer films between their neutral and
3
3
fully doped states at given wavelengths. The electrochromic
switching behaviors of the polymers were performed at regular
intervals of 5 s in a monomer free DCM solution containing
6
0.1 M TBAPF as a supporting electrolyte. Fig. 7 shows the
stabilities, optical contrasts and response times upon electro-
chromic switching of the polymer films at different wavelengths.
In these studies, the optical contrast (DT%) of the polymer films
which can be defined as the transmittance difference between
30
the redox states was recorded at constant wavelengths. Response
time, another most important characteristic of electrochromic
materials, is the time necessary for 95% of the full optical switch
34
(after which the naked eye could not sense the color change).
Table 2 The colorimetry analysis of the three polymers in reduced,
neutral and oxidized states
CIELAB 1976 (L*a*b*)
E, vs.
CIE 1931 color
coordinates
Polymer (Ag wire) (V) L*
a*
b*
PPTQ
0
1
47.01
48.56 ꢀ11.31
60.0 8.60
48.01 ꢀ6.78
4.88 ꢀ15.80 x = 0.28; y = 0.28
.4
ꢀ9.67 x = 0. 26; y = 0.31
7.53 x = 0.35; y = 0.34
ꢀ4.51 x = 0.28; y = 0.32
ꢀ1.4
0
PPBTQ
PPETQ
1
.4
36.56
67.74
59.57
79.78
11.31 ꢀ23.87 x = 0.26; y = 0.23
ꢀ
1.5
ꢀ0.2
36.65
12.21
4.072
6.24 x = 0.39; y = 0.31
25.16 x = 0.40; y = 0.38
7.527 x = 0.32; y = 0.35
4.09 x = 0.24; y = 0.39
Fig. 7 Electrochromic switching under an applied square voltage signal
for (a) PPTQ at 1230 nm, (b) PPBTQ at 336 and 1340 nm, and (c) PPETQ at
454, 1430 and 1800 nm with a residence time of 5 s.
1.2
ꢀ1.4
51.61 ꢀ39.37
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times of 0.75 s from the reduced to oxidized state and 2.5 s from onset oxidation potential and the resultant poly[2,3-di(2-pyridyl)-5,8-
the oxidized to reduced state at 336 nm, and in the NIR region bis(2-(3,4-ethylenedioxythienyl))quinoxaline] has the lowest band
(1340 nm), the response times were 2.35 s from the reduced to gap. To the best of our knowledge, this is the first example of
oxidized state and 1.05 s from the oxidized to reduced state. electropolymerized materials, poly[2,3-di(2-pyridyl)-5,8-bis(2-(3,4-
The dynamic electrochromic experiment for the PPETQ film ethylenedioxythienyl))quinoxaline], which exhibits a green color
was carried out at 454 nm, 1430 nm and 1800 nm. The potential in the reduced state, yellow color in the neutral state, and a
was interchanged between ꢀ0.2 V and 1.2 V at regular intervals colorless highly transmissive state in the oxidation state. As the
of 5 s. The DT% of PPETQ was calculated to be 31.8% at donor–acceptor–donor type p-conjugated polymers, they all
454 nm, 77.6% at 1430 nm and 80.3% at 1800 nm, as shown showed high optical contrasts (DT%), fast response times and
in Fig. 7c. The response times of PPETQ were 1.45 s from the excellent cyclic voltammetry stabilities. What is more, the gen-
reduced to oxidized state and 2.63 s from the oxidized to eration of redox waves in CV at negative potentials and variation
reduced state at 454 nm, 1.83 s from the reduced to oxidized of the spectral absorption curves upon reduction proved that all
state and 1.74 s from the oxidized to reduced state at 1430 nm, three polymers have stable n-doping properties. The polymer
and 0.78 s from the reduced to oxidized state and 1.25 s from films with their excellent electrochemical and optical properties
the oxidized to reduced state at 1800 nm. As to the difference are expected to be useful for practical use in electrochromic
in the response times at different wavelengths for each polymer display applications.
film, it is probably due to the different switching modes at different
wavelengths between the doping and dedoping processes. From the
data, it can be clearly found that PPETQ has better stability and
Acknowledgements
higher percent transmittance contrast than those of PPTQ and
The work was financially supported by the National Natural
PPBTQ after regular switching for 300 s. PPBTQ and PPETQ have
Science Foundation of China (51473074 and 31400044), China
outstanding optical contrasts in the NIR region, which is a very
Postdoctoral Science Foundation (2013M530397 and 2014T70861),
important property for various NIR applications, such as for
the Fundamental Research Funds for the Central Universities
polymer based field-effect transistors and camouflage devices.
(
14CX06105A) and the Natural Science Foundation of Shandong
The coloration efficiency (CE) is also an important characteristic
of electrochromic materials. CE can be calculated by using the
equation given below:
Province (ZR 2014JL009).
3
5
ꢀ
ꢁ
Tb
Tc
DOD
Notes and references
DOD ¼ log
and Z ¼ DQ
1
E. C. Rios, A. V. Rosario, A. F. Nogueira and L. Micaronic,
where T
b
and T
c
are the transmittances before and after coloration,
Sol. Energy Mater. Sol. Cells, 2010, 94, 1338–1345.
respectively. DOD is the change in the optical density, which is
proportional to the amount of created color centers. Z denotes the
coloration efficiency (CE). DQ is the amount of injected charge per
unit sample area. Using the above equation, the value of CE was
2 J. Huang, X. Wang, A. J. deMello, J. C. deMello and
D. D. C. Bradley, J. Mater. Chem., 2007, 17, 3551–3554.
3 Y. J. Zhang, K. Wang, G. L. Zhuang, Z. Q. Xie, C. Zhang,
F. Cao, G. X. Pan, H. F. Chen, B. Zou and Y. G. Ma, Chem. –
Eur. J., 2015, 21, 2474–2479.
4 Y. J. Zhang, J. W. Sun, G. L. Zhuang, M. Ouyang, Z. W. Yu,
F. Cao, G. X. Pan, P. S. Tang, C. Zhang and Y. G. Ma, J. Mater.
Chem. C, 2014, 2, 195–200.
5 C. M. Hangarter, M. Bangar, A. Mulchandania and
N. V. Myung, J. Mater. Chem., 2010, 20, 3131–3140.
6 K. R. Lee and G. A. Sotzing, Chem. Commun., 2013, 49,
5192–5194.
7 A. Cihaner and F. Algl, Adv. Funct. Mater., 2008, 18,
3583–3589.
2
ꢀ1
measured to be 252.4 cm C at 1230 nm for PPTQ. And for the
2
ꢀ1
film PPBTQ it was measured to be 192.9 cm C at 336 nm and
2
ꢀ1
2
ꢀ1
4
02.9 cm C at 1340 nm. For PPETQ, the data were 114.2 cm C
at 454 nm, 202.8 cm C at 1430 nm and 202.3 cm C at
800 nm. These values are comparable with some newly reported
2
ꢀ1
2
ꢀ1
1
36
D–A type polymers derived from quinoxaline derivatives. Based on
the above discussions, we can say that the distinct optical contrast,
fast switching times and satisfactory CE values make these three
polymer films promising electrochromic materials for smart
windows, especially in the case of PPETQ.
8
C. M. Amb, A. L. Dyer and J. R. Reynolds, Chem. Mater.,
011, 23, 397–415.
2
Conclusions
9
G. E. Gunbas, A. D urmus and L. Toppare, Adv. Mater., 2008,
20, 691–695.
In this study, three monomers based on 2,3-di(2-pyridyl)quinoxaline
as the acceptor unit and three thiophene derivatives as the donor 10 Z. Xu, M. Wang, J. S. Zhao, C. S. Cui, W. Y. Fan and J. F. Liu,
units were synthesized to understand the effects of electron- Electrochim. Acta, 2014, 125, 241–249.
donating abilities of the donor unit on the electrochemical and 11 P. M. Beaujuge, S. Ellinger and J. R. Reynolds, Nat. Mater.,
spectroelectrochemical properties of the resulting electropolymerized 2008, 7, 795–799.
materials. Due to the stronger electron donating ability of the 12 R. C. Coffin, J. Peet, J. Rogers and G. C. Bazan, Nat. Chem.,
,4-ethylenedioxythiophene unit, the 2,3-di(2-pyridyl)-5,8-bis(2- 2009, 1, 657–661.
3,4-ethylenedioxythienyl))quinoxaline monomer has the lowest 13 S. Hayashi and T. Koizumi, Polym. Chem., 2012, 3, 613–616.
3
(
New J. Chem.
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View Article Online
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Paper
1
4 D. M. Welsh, L. J. Kloeppner, L. Madrigal, M. R. 25 M. Ak, M. S. Ak, G. Kurtay, M. G u¨ ll u¨ and L. Toppare, Solid
Pinto, B. C. Thompson, K. S. Schanze, K. A. Abbound, State Sci., 2010, 12, 1199–1204.
D. Powell and J. R. Reynolds, Macromolecules, 2002, 35, 26 H. T. Liu, Y. Z. Li, J. K. Xu, Z. G. Le, M. B. Luo, B. S. Wang,
517–6525. S. Z. Pu and L. Shen, Eur. Polym. J., 2008, 44, 171–188.
5 A. Cirpan, A. A. Argun, C. R. G. Grenier, B. D. Reeves and 27 J. K. Xu, J. Hou, S. S. Zhang, Q. Xiao, R. Zhang, S. Z. Pu and
J. R. Reynolds, J. Mater. Chem., 2013, 13, 2422–2428. Q. L. Wei, J. Phys. Chem. B, 2006, 110, 2643–2648.
6 A. Durmus, G. E. Gunbas and L. Toppare, Chem. Mater., 28 D. M. de Leeuw, M. M. J. Simenon, A. R. Brown and
007, 19, 6247–6251. R. E. F. Einerhand, Synth. Met., 1997, 87, 53–59.
7 G. E. Gunbas, A. Durmus and L. Toppare, Adv. Funct. Mater., 29 J. H. wang, J. I. Son and Y. B. Shim, Sol. Energy Mater. Sol.
008, 18, 2026–2030. Cells, 2010, 94, 1286–1292.
8 E. Karabiyik, E. Sefer, F. B. Koyuncu, M. Tonga, E. Ozdemir 30 W. Yang, J. S. Zhao, Y. Kong, T. Y. Kong and C. S. Cui, Int.
and S. Koyuncu, Macromolecules, 2014, 47, 8578–8584. J. Electrochem. Sci., 2012, 7, 2764–2780.
9 E. Sefer, S. O. Hacioglu, M. Tonga, L. Toppare, A. Cirpan and 31 C. A. Thomas, K. Zong, K. A. Abboud, P. J. Steel and
S. Koyuncu, Macromol. Chem. Phys., 2015, 216, 829–836. J. R. Reynolds, J. Am. Chem. Soc., 2004, 126(50), 6440.
0 S. J. Chen, Y. Zhang, J. W. Gu, M. L. Ma, L. Zhang, J. Zhou 32 E. Yildiz, P. Camurlu, C. Tanyeli, I. Akhmedov and
and Y. Y. Zhou, eXPRESS Polym. Lett., 2012, 6(6), 454–464. L. Toppare, J. Electroanal. Chem., 2008, 612, 247–256.
1 Y. Tsubata, T. Suzuki, T. Miyashi and Y. Yamashita, J. Org. 33 E. Sefer, F. B. Koyuncu, E. Oguzhan and S. Koyuncu,
Chem., 1992, 57, 6749–6755. J. Polym. Sci., Part A: Polym. Chem., 2010, 48, 4419–4427.
2 L. H. Xu, C. Su, C. Zhang and C. A. Ma, Synth. Met., 2011, 34 B. Yigitsoy, S. Varis, C. Tanyeli, I. M. Akhmedov and
61, 1856–1860. L. Toppare, Electrochim. Acta, 2007, 52, 6561–6568.
3 E. M. Genies, G. Bidan and A. F. Diaz, J. Electroanal. Chem., 35 S. J. Yoo, J. H. Cho, J. W. Lim, S. H. Park, J. Jang and
983, 149, 101–113. Y. E. Sung, Electrochem. Commun., 2010, 12, 164–167.
4 S. Tarkuc, Y. A. Udum and L. Toppare, Polymer, 2009, 50, 36 Y. X. Liu, M. Wang, J. S. Zhao, C. S. Cui and J. F. Liu, RSC
458–3464. Adv., 2014, 4, 52712–52726.
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