A novel poly(aryl ether) containing azobenzene chromophore and pendant oligoaniline: Synthesis and electrochromic properties

Article abstract of DOI:10.1016/j.electacta.2011.11.052

A novel poly(aryl ether), containing pendant oligoaniline and azobenzene moieties (Azo-PAE-p-OA), was synthesized by nucleophilic polycondensation. The structures were confirmed spectroscopically via nuclear magnetic resonance (NMR) and Fourier-transform infrared spectra (FTIR), morphological data was ascertained via X-ray diffraction (XRD), and the thermal stability was probed via thermogravimetric analysis (TGA). Due to the coexistence of oligoaniline and azobenzene groups, Azo-PAE-p-OA shows reversible electroactivity and expectable photoresponse to light irradiation, chemical redox and electrochemical modulation. The electrochromic performance of a Azo-PAE-p-OA film on indium tin oxide (ITO) was investigated by spectrochronoamperometry, and exhibited electrochromic properties with high contrast value, good coloration efficiency, moderate switching times, and acceptable stability.

Full text of DOI:10.1016/j.electacta.2011.11.052

Electrochimica Acta 60 (2012) 253–258
Contents lists available at SciVerse ScienceDirect
Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
A novel poly(aryl ether) containing azobenzene chromophore and pendant
oligoaniline: Synthesis and electrochromic properties
Danming Chaoa,b, Tian Zheng , Hongtao Liu , Rui Yang , Xiaoteng Jia , Shutao Wang ,
Erik B. Berda , Ce Wang
a
a
a
a
a
a
b,∗
a,∗∗
Alan G. MacDiarmid Institute, College of Chemistry, Jilin University, Changchun 130012, PR China
Department of Chemistry and Materials Science Program, University of New Hampshire, Durham, NH 03824, USA
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 October 2011
Received in revised form 9 November 2011
Accepted 11 November 2011
Available online 22 November 2011
A novel poly(aryl ether), containing pendant oligoaniline and azobenzene moieties (Azo-PAE-p-OA),
was synthesized by nucleophilic polycondensation. The structures were confirmed spectroscopically via
nuclear magnetic resonance (NMR) and Fourier-transform infrared spectra (FTIR), morphological data
was ascertained via X-ray diffraction (XRD), and the thermal stability was probed via thermogravimet-
ric analysis (TGA). Due to the coexistence of oligoaniline and azobenzene groups, Azo-PAE-p-OA shows
reversible electroactivity and expectable photoresponse to light irradiation, chemical redox and elec-
trochemical modulation. The electrochromic performance of a Azo-PAE-p-OA film on indium tin oxide
Keywords:
Electroactive polymer
Polyaniline
Electrochromic
Pendant
(ITO) was investigated by spectrochronoamperometry, and exhibited electrochromic properties with
high contrast value, good coloration efficiency, moderate switching times, and acceptable stability.
© 2011 Elsevier Ltd. All rights reserved.
Oligoaniline
1
. Introduction
Electrochromic devices exhibit reversible and visible changes
improvement in electrochromic contrast were reported [13,14]. Tu
et al. prepared electrochromic devices by PANI derivatives (poly(o-
anisidine) and poly(o-anisidine-co-o-nitroaniline)) and compared
them electrochromic performance [15]. Sonavane et al. and Zhou
et al. studied multicolor electrochromic devices based on PANI that
exhibited high electrochromic contrast and coloration efficiency
[16,17].
in their transmission and reflection due to variations in the redox
states [1–3], and can be used as large area displays, smart mirrors
and windows [4]. Many electrochromic devices have been previ-
ously investigated based on a variety of organic [5] and inorganic
materials [1] and conducting polymers [6,7]. The high contrast
value in the optical absorption spectrum of conducting polymers
makes these materials prime candidates for electrochromic devices
Although PANI/polyacid composites, PANI derivatives and PANI
blends have been widely used for electrochromic devices, its full
utilization is dependent on advancements to improve its inher-
ent shortcomings in solubility and processability. So it can be
envisioned that electroactive polymers bearing oligoaniline groups
with excellent film forming ability and solubility should be a highly
competitive candidate for an electrochromic device. Recently, con-
siderable effort has been devoted toward synthesizing electroactive
polymers containing oligoaniline groups, such as graft [18–20],
alternating [21–23], block-like [24,25], star-like [26] and network
[27] polymers. To the best of our knowledge, only a few elec-
trochromic devices prepared from these electroactive polymers
have been presented [20,21,28].
[
8]. Among conducting polymers, polyaniline (PANI) has been
extensively studied for electrochromic application due to its unique
optical properties, excellent switching speed, and high environ-
mental stability. Many PANI-based electrochromic devices have
recently been reported. Hu et al. studied the electrochromic proper-
ties of PANI–poly(2-acrylamido-2-methyl-1-propanosulfonic acid)
composite thin films, which exhibited a lower optical switching
voltage and higher contrast value [9,10]. Some other PANI/polyacid
composites used as electrochromic devices have also been inves-
tigated and reported [11,12]. The method of layer-by-layer
assembly was been applied to prepare electrochromic devices and
Recently azobenzene-containing polymers have attracted con-
siderable attention because of their variety of photoreponsive
properties, such as photoinduced birefringence and dichroism
[
29,30], optical switching [31], and photoinduced surface-relief-
∗
Corresponding author. Tel.: +1 603 862 1762; fax: +1 603 862 4278.
Corresponding author. Tel.: +86 431 85168292; fax: +86 431 85168292.
E-mail addresses: Erik.Berda@unh.edu (E.B. Berda), cwang@jlu.edu.cn,
grating (SRG) formations [32,33]. Due to its properties as a dye,
azobenzene group has been usually introduced to construct multi-
color electrochromic device [34–36], which generally have a great
∗
∗
chaodanming@jlu.edu.cn (C. Wang).
0
013-4686/$ – see front matter © 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2011.11.052

2
54
D. Chao et al. / Electrochimica Acta 60 (2012) 253–258
contrast value. Here, we reported the synthesis of a novel poly(aryl
ether) containing pendant oligoaniline and azobenzene moieties
–CONH–), ı = 7.80 (s, 1H, due to –NH–), ı = 7.77 (s, 1H, due to –NH–),
ı = 7.65 (s, 1H, due to –NH–), ı = 7.56 (t, 1H, due to Ar–H), ı = 7.48 (d,
2H, due to Ar–H), ı = 7.23 (t, 2H, due to Ar–H), ı = 7.14 (t, 2H, due to
Ar–H), ı = 6.96 (m, 12H, due to Ar–H), ı = 6.68 (t, 1H, due to Ar–H).
(
Azo-PAE-p-OA) by nucleophilic polycondensation and its perfor-
mance in an electrochromic device.
ꢀ
2
. Experimental
2.4. Synthesis of 4,4 -dihydroxyazobenzene
2.1. Materials
Potassium hydroxide (100 g), 4-nitrophenol (20 g) and water
(
20 mL) was added into a 500 mL three-necked round-bottom flask
◦
N-phenyl-p-phenylenediamine,
2,6-difluorobenzoyl
chlo-
and heated to 150 C with mechanical stirring for 2 h. The mixture
was heated to 195 C with blowing off bubble. After the comple-
◦
ride and 4-nitrophenol were purchased from Aldrich.
ꢀ
4
,4 -Dichlorodiphenylsulfone and potassium hydroxide were
tion of the reaction, the obtained mixture was cooled to room
temperature and dissolved in the 200 mL water. Adjusted the pH
of the solution by adding of dilute hydrochloric acid and yield-
ing an orange precipitate which was recrystallized twice from
ethanol/H2O (1:1) to give a product of red crystals, followed by
drying under dynamic vacuum at room temperature for 24 h (30%
yield).
purchased from Shanghai Chemical Factory. K CO was dried
2
3
◦
at 110 C for 24 h before used. All other reagents were obtained
from commercial sources and used as received without further
purification. Distilled and deionized water was used.
2
.2. Measurement
MALDI-TOF-MS: m/z calculated for C12H10N O = 214.2. Found
2
2
−
1
Mass spectroscopy (MS) was performed on an AXIMA-CFR
215.1. FTIR (KBr, cm ): 3377 (m, ꢁOH), 1589 (vs, ꢁ
C
C of benzenoid
laser desorption ionization flying time spectrometer (COMPACT).
Fourier-transform infrared spectra (FTIR) measurements were
recorded on a BRUKER VECTOR 22 Spectrometer by averaging 128
rings), 1500 (m, ꢁ
C
C of benzenoid rings), 1425 (m, ꢁ
N
N), 842 (s,
1
ıCH), 766 (w, ıCH), 644 (w, ıCH). H NMR (d6-DMSO): ı = 10.12 (s,
2H, due to –OH), ı = 7.71 (d, 4H, due to Ar–H adjacent to azo group),
ı = 6.91 (d, 4H, due to Ar–H adjacent to hydroxy group).
−1
−1
scans at a solution of 4 cm in the range of 4000–400 cm . The
nuclear magnetic resonance spectra (NMR) of 2,6-difluorobenzoyl
ꢀ
aniline tetramer, 4,4 -dihydroxyazobenzene and Azo-PAE-p-OA in
2.5. Synthesis of Azo-PAE-p-OA
deuterated dimethyl sulfoxide (DMSO) were run on a BRUKER-500
spectrometer to determine the chemical structure and tetram-
ethylsilane was used as the internal standard. The number-average
molecular weight (Mn), weight-average molecular weight (Mw),
and molecular weight distribution of Azo-PAE-p-OA were mea-
sured with a gel permeation chromatography (GPC) instrument
equipped with a Shimadzu GPC-802D gel column and SPD-M10AVP
A typical polymer synthesis procedure is as follows. A mix-
ture of NMP (30 mL), toluene (10 mL), anhydrous potassium
carbonate (1.451 g), 2,6-difluorobenzoyl aniline tetramer (1.013 g,
ꢀ
ꢀ
2 mmol), 4,4 -dichlorodiphenylsulfone (2.297 g, 8 mmol), and 4,4 -
dihydroxyazobenzene (2.142 g, 10 mmol) were added to a 100 mL
three-necked round-bottom flask and heated to reflux under nitro-
gen with magnetic stirring for 2 h to remove the water by azeotropic
distillation with toluene, and then the toluene was removed. The
mixture was heated to reflux for 8 h to ensure the completion of the
reaction. The solution was cooled to room temperature and poured
into 200 mL water, which yielded a yellow precipitate. The precipi-
tate was washed with water and ethanol several times, filtered and
ꢀ
detector with N,N -dimethylformamide as an eluent at a flow
−1
rate of 1 mL min . Calibration was accomplished with monodis-
persed polystyrene (PS) standards. X-ray powder diffraction (XRD)
patterns of Azo-PAE-p-OA were recorded on a Siemens D5005
diffractometer using Cu K␣ radiation. Perkin-Elmer PYRIS 1 TGA
was used to investigate the thermal stability of Azo-PAE-p-OA
◦
◦
◦
in the temperature range from 100 C to 700 C at a rate of
dried under dynamic vacuum at 40 C for 24 h (93% yield).
◦
−1
1
0.0 C min
under nitrogen protection. Photoisomerization of
Azo-PAE-p-OA in a DMAc solution and/or spin-coated thin film
were conducted using high pressure mercury lamp in conjunc-
tion with band-pass UV filter (ꢀmax = 360 nm). UV–vis spectra were
performed on UV-2501 PC Spectrometer (SHIMADZU) in dilute
DMAc solution. The CV was investigated on a CHI 660A Electro-
chemical Workstation (CH Instruments, USA) with a conventional
three-electrode cell, using a Ag/AgCl as the reference electrode,
a platinum wire electrode as the counter electrode, and a glassy
carbon electrode (GCE, ˚ 3.0 mm) as the working electrode. Spec-
troelectrochemical measurements were carried out in a cell built
from a 1 cm commercial cuvette using a UV-2501 PC Spectrom-
eter (SHIMADZU). The ITO-coated glass was used as the working
electrode, a Pt wire as the counter electrode, an Ag/AgCl cell as
2.6. Fabrication of electrochromic electrode
The ITO substrates were washed ultrasonically in ethanol for
5 min and then in the deionized water for another 5 min, followed
by drying in the air before use. Azo-PAE-p-OA (0.03 g) was dis-
solved in 1 mL DMAc to form a dark brown solution, and filtered
through 0.2-␮m poly(tetrafluoroethylene) syringe filter. Then, Azo-
PAE-p-OA films were spin-coated onto the ITO substrates using
the DMAc solution of Azo-PAE-p-OA. The spin-coating process
started at 500 rpm for 5 s and then 1000 rpm for 30 s. A copper
tape (1.0 cm × 0.5 cm) was applied to the top edge of ITO substrates,
before electrochromic measurements, as the bus bar.
the reference electrode and 0.5 mol/L H SO4 was used as the elec-
3. Results and discussion
2
trolyte.
3.1. Synthesis and characterization of Azo-PAE-p-OA
2.3. Synthesis of 2,6-difluorobenzoyl aniline tetramer
The synthetic procedure for Azo-PAE-p-OA is depicted
The synthesis of 2,6-difluorobenzoyl aniline tetramer was con-
in Scheme 1. The polymerization proceeded by K CO -
2 3
ducted according to the literature [20].
mediated nucleophilic aromatic polycondensation using
ꢀ
MALDI-TOF-MS: m/z calculated for C31H24F N O = 506.5. Found
4,4 -dihydroxyazobenzene as bisphenol monomer. The ratio of 2,6-
2
4
−1
ꢀ
5
06.6. FTIR (KBr, cm ): 3369 (s, ꢁNH), 3299 (s, ꢁNH), 1657 (vs,
difluorobenzoyl aniline tetramer to 4,4 -dichlorodiphenylsulfone
◦
ꢁC O), 1600 (s, ꢁC C of benzenoid rings), 1525 (vs, ꢁC C of ben-
is about 0.2:0.8. The reaction temperature was held at 140 C to
zenoid rings), 1303 (s, ꢁC–N), 1008(m, ıCF), 817 (m, ıCH), 746 (m,
remove the water by azeotropic distillation with toluene, and then
increased to 200 C to facilitate the polymerization. The chemical
1
◦
ıCH), 692 (m, ıCH). H NMR (d -DMSO): ı = 10.51 (s, 1H, due to
6

D. Chao et al. / Electrochimica Acta 60 (2012) 253–258
255
O
S
O
NMP/Toluene
K CO
0
.2 F
F + 0.8 Cl
Cl + HO
N
N
OH
2
3
O C
HN
H
N
3
O
S
O
N
N
O
O
N
N
O
O
C
O
0
.2
0.8
HN
H
N
H
H
N
N
Scheme 1. Synthesis of electroactive Azo-PAE-p-OA.
structure of Azo-PAE-p-OA was confirmed by FTIR, 1H NMR spec-
troscopy, GPC and XRD. FTIR spectra of Azo-PAE-p-OA showed the
characteristic absorption bonds around 3386 cm corresponding
bulky pendant oligoaniline groups decrease the interchain hydro-
gen bonding and ␲–␲ interactions and disturb the close packing
and regularity of the polymer chains. The amorphous structure is
a basic requirement for polymers used in optoelectronic devices,
because aggregation and microcrystallization will greatly affect
stability and uniformity of the device.
−
1
−
1
to N–H stretching vibration, around 3062 cm
stretching vibration of aryl groups and around 1670 cm due to
O stretching vibration of aryl carbonyl groups. The vibration at
based on C–H
−
1
C
−1
−1
around 1583 cm and 1489 cm is attributed to the stretching
vibration of C C of the benzene rings, and the peak at 1240 cm
can be assigned to the stretching vibration of C–O–C of the aryl
ether linkages. The bands at 1296 cm (ꢁC–N), 835 cm (ıCH), and
92 cm (ıCH), based on the structure of oligoaniline, were also
The thermal properties of Azo-PAE-p-OA were evaluated by TGA
−
1
◦
(Fig. 2). A single stage mass loss beginning at 310 C is observed
corresponding to the decomposition of main chain. Weight loss
temperatures of the obtained polymer for a loss of 5% and 10%
−1
−1
−1
◦
◦
6
are 350 C and 381 C, respectively. This indicates that the obtained
polymer has good thermal stability and higher degradation tem-
perature than the usual polyaniline materials [37].
−1
−1
found. And the bands at 1147 cm (ꢁO S O), 1103 cm (ıCH), and
50 cm (ıCH) were attributed to the vibrations of diphenylsufone
−1
5
1
segment. In the H NMR spectra of Azo-PAE-p-OA, the signals at
ı = 10.25 ppm are attributed to the amino protons and the signals
around ı = 7.98 ppm are ascribed to the aryl protons adjacent to
the diphenylsufone groups, the integral area ratio of the two peaks
is near 1:16, which indicates that the Azo-PAE-p-OA has been
synthesized according to expectation. Furthermore, other aro-
matic protons appeared at ı = 7.37–6.59. All of the 1H NMR signals
support the proposed molecular structure of Azo-PAE-p-OA. The
number average molecular weight (Mn) and the polydispersity
index of Azo-PAE-p-OA, obtained by GPC, are 51,400 and 1.66,
respectively. Moreover, Azo-PAE-p-OA exhibited outstanding
solubility in polar solvents such as THF, DMF, DMAc, DMSO and
NMP, due in part to the bulky pendant groups, which can impede
the interchain entanglement to some extent.
3
.2. Spectroscopic properties of Azo-PAE-p-OA by chemical
oxidation
The optical properties of the Azo-PAE-p-OA were investigated
by UV–vis spectroscopy. A small amount of Azo-PAE-p-OA was dis-
solved in DMAc solution followed by the addition of trace amount
of (NH ) S O . This oxidation process was monitored by UV–vis
4
2
2
8
spectra with time intervals at about 4 min; the obtained UV–vis
spectra are presented in Fig. 3. First, the absorption peaks at 347 nm
were observed, which are associated with ␲–␲* transitions in the
benzoid rings and trans-azobenzene groups [38–40]. When slow
oxidation took place, the absorption peak at 347 nm started to
undergo a red shift (from 347 nm to 353 nm) while decreasing
in intensity. Then the UV–vis spectra showed a new absorption
peak at about 590 nm. This has been assigned to the exciton-type
The wide-angle XRD patterns of Azo-PAE-p-OA (Fig. 1) show a
◦
◦
broad peak from 10 to 30 , which is characteristic of the diffrac-
tion by an amorphous polymer. It is mainly due to the fact that the
1
00
8
6
4
2
000
000
000
000
0
9
8
7
6
5
0
0
0
0
0
100
200
300
400
500
600
700
1
0
20
30
40
50
60
2θ/degrees
Temperature (ºC)
Fig. 1. The wide-angle XRD patterns of Azo-PAE-p-OA.
Fig. 2. TGA thermograms of Azo-PAE-p-OA in N2.

2
56
D. Chao et al. / Electrochimica Acta 60 (2012) 253–258
1.5
1.2
0.9
0.6
0.3
0.0
1
1
0
0
0
.5
.2
.9
.6
.3
a
b
0.0
3
00
400
500
600
700
800
300
400
500
600
700
800
Wavelength (nm)
Wavelength (nm)
Fig. 3. UV–vis spectra monitoring the chemical oxidation of Azo-PAE-p-OA. (a) From the leucoemeraldine base to the emeraldine base and (b) from the emeraldine base to
the pernigraniline base.
transition between the HOMO orbital of the benzoid ring and the
LUMO orbital of the quinoid ring [41] and continually increased in
intensity. When its intensity reached the maximum, the Azo-PAE-
p-OA was in the emeraldine oxidation state with the parent aniline
tetramer segment containing one quinoid ring. With further oxi-
dization of Azo-PAE-p-OA, all the absorption peaks decreased and
finally absorption in the 400 nm and 800 nm range disappeared,
which showed that the Azo-PAE-p-OA has reached in the pern-
igraniline oxidation state with parent aniline tetramer segment
containing two quinoid rings. The chemical oxidation process of
Azo-PAE-p-OA is similar to that of polyaniline and its derivatives
DMAc solution at about 347 nm, associated with the ␲–␲* transi-
tion of the trans-azobenzene groups and benzoid rings, gradually
decreased as irradiation time increased. This occurred concurrently
with a blue shift, due to the trans-to-cis photoisomerization process
of the azobenzene chromophore. The blue shift of the absorp-
tion was attributed to the overlap of the ␲–␲* transition of the
trans-azobenzene groups and benzoid rings [35,40]. UV–vis spec-
tra changes were obtained with time intervals about 2 min and the
trans-cis isomerization reached to a steady state 10 min later, then
the above solution was transferred to visible radiation. As shown
in Fig. 4(b), the intensity of the absorption, associated with ␲–␲*
transition of the trans-azobenzene group, gradually increased with
the anticipated red shift. The absorption at about 347 nm nearly
reached the intensity of original values after 18 min. Photoisomer-
ization of Azo-PAE-p-OA thin film were given in Fig. 4(c) and (d),
which also presented a similar reversibility to those in solution.
However, the absorption peak associated with ␲–␲* transition for
the thin film red-shifted to 350 nm, due to the solvachromic effect
of azobenzene group. In addition, the time for the film to reach a
photostationary state was little shorter than in solution, because
[
22,23].
3.3. Photoisomerization of Azo-PAE-p-OA
Trans-cis isomerization of Azo-PAE-p-OA in leucoemeraldine
oxidation state was investigated by irradiating the DMAc solution
and spin-coated thin film, respectively. The UV–vis spectra changes
were monitored during the ultraviolet and visible irradiation. As
shown in Fig. 4(a), the intensity of the absorption of Azo-PAE-p-OA
1.5
1.2
0.9
0.6
0.3
0.0
1.5
1.2
0.9
0.6
0.3
0.0
Ultraviolet Light
Visible Light
a
b
0
2
4
6
8
min
min
min
min
min
0 min
2 min
4 min
6 min
8 min
10 min
10 min
12 min
14 min
16 min
18 min
3
00
400
500
600
700
800
300
400
500
600
700
800
Wavelength (nm)
Wavelength (nm)
c
d
Visible Light
Ultraviolet Light
0
0
0
0
.9
.6
.3
0.9
0.6
0.3
0.0
0
2
4
6
8
min
min
min
min
min
0 min
1 min
3 min
6 min
10min
.0
3
00
400
500
600
700
800
300
400
500
600
700
800
Wavelength (nm)
Wavelength (nm)
Fig. 4. UV–vis spectra changes of Azo-PAE-p-OA with the different irradiation time: (a and b) in DMAc solution and (c and d) as spin-coated film.

D. Chao et al. / Electrochimica Acta 60 (2012) 253–258
257
0
0
0
.010
.005
.000
1
00 mV/s
1
0 mV/s
0.012
.008
.004
0.000
0.004
0
0
-
-
0.005
0.010
-
-0.008
-0.012
2
0
40
60
80
100
Scan Rates (mV/s)
Fig. 6. The spectral changes of Azo-PAE-p-OA/ITO electrode (0.6 cm × 3 cm) in
0
.5 mol/L H2SO4 at different potentials. Inset shows photographs of the Azo-PAE-
0
200
400
600
800
1000 1200
p-OA/ITO electrode at different potentials.
Potential (mV) vs.Ag/AgCl
H SO coupled with applied potentials of −0.2, 0, 0.2, 0.4, 0.6,
Fig. 5. Cyclic voltammograms of Azo-PAE-p-OA electrode in 1 mol/L H2SO4 at dif-
ferent potential scan rates: 10–100 mV s . Inset shows the relationships between
the oxidation peaks and reduction current vs. potential scan rate.
2
4
−1
0.8 and 1.0 V (vs. Ag/AgCl). It is clear from Fig. 6, the Azo-PAE-
p-OA film shows different UV–vis absorption spectra at various
applied potentials. The optical constrast value (%ꢂT) was found
to be 25% at 700 nm measured between its coloring and bleaching
states. The color of the Azo-PAE-p-OA thin films changed drasti-
cally from a transmissive yellow (at −0.2 V), to green (at 0.4 V),
and finally to an absorptive brown blue (at 0.8 V) (inset of Fig. 6).
In conclusion, as a multicolor electrochromic material with color
changing from yellow to blue, Azo-PAE-p-OA would have a wider
application in an electrochromic device compared with polyaniline
materials.
of the relative lower concentration of Azo-PAE-p-OA. Those results
confirm that Azo-PAE-p-OA retained the photoisomerization char-
acteristics of azobenzene.
3.4. Electrochemical activity
Fig. 5 shows the cyclic voltammetry of Azo-PAE-p-OA using
Ag/Ag+ as the reference electrode in 1.0 M H SO at differ-
2
4
−1
ent potential scan rates (10–100 mV s ). The DMAc solution of
Azo-PAE-p-OA was cast on the g-c working electrode and was
evaporated to form a thin solid film. Under these conditions,
the cyclic voltammetry of Azo-PAE-p-OA showed two redox pro-
cesses with the oxidation peaks at 350 and 500 mV, which were
respectively assigned to the transition of leucoemeraldine base
Besides the optical constrast value (%ꢂT), the switching time
and the electrochromic efficiency are usually used to evaluate
the electrochromic devices. The electrochromic performances of
Azo-PAE-p-OA were recorded by spectrochronoamperometry in
the optical contrast at 700 nm during repeated potential stepping
between reductive (−0.2 V) and oxidative state at 0.8 V with a
residence time of 30 s. Fig. 7 presents the results for the first 5
cycles. The switching time is the time required to bring Azo-PAE-
p-OA to its reduced state from its oxidized state or vice versa.
Here, it is defined as the time required for reaching 95% of the
full change in coloring/bleaching process. The Azo-PAE-p-OA film
required a switching time of 3.3 s at 0.8 V for the coloring process at
700 nm and 1.4 s at −0.2 V for bleaching. The coloration efficiency
CE (ꢃ = ꢂOD/Q) is a practical tool for measuring the power require-
ments of an electrochromic material. The electrochromic behavior
(
LEB)/emeraldine base (EB), and emeraldine base/pernigraniline
base (PNB). A linear dependence of the peak currents, as a func-
−
1
tion of scan rates in the region of 10–100 mV s (inset of Fig. 5),
confirmed both a surface controlled process [42] and that the elec-
troactive polymer film was well-adhered. The good adherence of
the Azo-PAE-p-OA, attribute to its poly(aryl ether) main chain
structure, makes it a good electrode material. The Azo-PAE-p-OA
film was found to be very stable, without change in CV diagram
after 30 repeated cyclic scans between 0 and 900 mV.
2
of Azo-PAE-p-OA exhibited CE up to 107.4 cm /C (at 700 nm) at
3
.5. Spectroelectrochemistry and electrochromic performances
the oxidation stage. Usually, electrochromic devices stability was
damaged drastically under the acid conditions, because the ITO
substrate would like to lose its conductivity in the acid. In our
test, to investigate the stability of the electrochromic device, the
Spectroelectrochemical studies were performed on the film
of Azo-PAE-p-OA spin-coated on the ITO glass slide in 0.5 mol/L
0
0
0
0
.6
.4
.2
.0
b
a
0
.12
0.08
0
0
.04
.00
-
-
-
0.2
0.4
0.6
1
2
3
4
5
101 102 103 104 105
1
2
3
4
5
101 102 103 104 105
Number of Cycles
Number of Cycles
Fig. 7. (a) Current consumption and (b) absorbance changes monitored at 700 nm of Azo-PAE-p-OA/ITO electrode in 0.5 mol/L H2SO4 for the first 5 and 101st-105th cycles
when the anodic potential was switched between −0.2 V and 0.8 V with a residence time of 30 s.

2
58
D. Chao et al. / Electrochimica Acta 60 (2012) 253–258
electrochromic performance was collected after 100 cycles of
potential switching. The switching time increased to 4.2 s at 0.8 V
for the coloring process and 2.0 s at −0.2 V for bleaching, and the
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This work has been supported in part by the National Natural
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