Fabrication of electrochemically responsive surface relief diffraction gratings based on a multifunctional polyamide containing oligoaniline and azo groups

Article abstract of DOI:10.1039/c1jm14047g

A novel, well-defined multifunctional polyamide bearing pendent aniline tetramer groups has been synthesized via low temperature solution polycondensation. The simultaneous presence of these two functional groups allows the polyamide to display the properties of azo-chromophore and oligoaniline, such as photoinduced birefringence and reversible electroactivity. The electrochromic performance of the polyamide shows the optical change in absorptivity depends on the various redox states of oligoaniline upon electrochemical switching. It is well known that a change in absorptivity is accompanied by a concomitant change in refractive index. By taking advantage of this effect and using the single step fabrication of surface relief gratings based on azo-chromophore, we have fabricated optical diffraction gratings with which the diffraction efficiency can be modulated by an electrochemical signal. Although patterned electroactive films have been made by many techniques, the copolymer approach employing the simple one-step surface relief gratings process displays optimal properties with respect to modulation depth and convenience, which avoids complicated electropolymerization steps or photochemical reactions. The electrochemically-induced modulation in the diffraction efficiency of the polyamide is believed to arise primarily from the effect of the redox state on the film's refractive index.

Full text of DOI:10.1039/c1jm14047g

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PAPER
Fabrication of electrochemically responsive surface relief diffraction gratings
based on a multifunctional polyamide containing oligoaniline and azo groups†
a
Xiaoteng Jia, Danming Chao,
ab
b
c
a
a
a
*
*
Erik B. Berda, Songhao Pei, Hongtao Liu, Tian Zheng and Ce Wang
Received 18th August 2011, Accepted 14th September 2011
DOI: 10.1039/c1jm14047g
A novel, well-defined multifunctional polyamide bearing pendent aniline tetramer groups has been
synthesized via low temperature solution polycondensation. The simultaneous presence of these two
functional groups allows the polyamide to display the properties of azo-chromophore and oligoaniline,
such as photoinduced birefringence and reversible electroactivity. The electrochromic performance of
the polyamide shows the optical change in absorptivity depends on the various redox states of
oligoaniline upon electrochemical switching. It is well known that a change in absorptivity is
accompanied by a concomitant change in refractive index. By taking advantage of this effect and using
the single step fabrication of surface relief gratings based on azo-chromophore, we have fabricated
optical diffraction gratings with which the diffraction efficiency can be modulated by an
electrochemical signal. Although patterned electroactive films have been made by many techniques, the
copolymer approach employing the simple one-step surface relief gratings process displays optimal
properties with respect to modulation depth and convenience, which avoids complicated
electropolymerization steps or photochemical reactions. The electrochemically-induced modulation in
the diffraction efficiency of the polyamide is believed to arise primarily from the effect of the redox state
on the film’s refractive index.
approaches in producing electroactive polymer periodic
arrays,14,15 most of these techniques either necessitate complex
steps or modified electrodes in electrochemical polymerization,
which would hamper the applications of the conducting poly-
mer pattern films.
Introduction
During the past few years, electroactive polymers have gained
exposure from their widespread applications in organic field-
effect transistors, photovoltaic cells, light emitting diodes, and
sensors.1–4 The patterning of an electroactive or conductive
polymer is often needed in the fabrication of microelectronic
or -photonic devices5 or microsensor arrays,6 which have
promising applications in microelectromechanical systems
(MEMS), biosensors, cell-growth regulation, and microfluidic
systems.7–9 Diffraction gratings of electroactive polymer thin
films are increasingly used as signal transduction layers in the
sensing of NADH,10 pH,11 etc, attributed to the fact that the
diffraction efficiency (DE) can be modulated with an electro-
chemical or chemical stimulus because of their reversible redox
properties. To date, patterned surfaces are normally produced
by toilful and sophisticated lithographic techniques or direct
photochemical patterning.12,13 Despite the success of these
Azobenzene functionalized polymers have been intensively
investigated for their photoresponsive properties and potential
applications in diffractive optical elements, information storage,
optical switching, sensors, and actuators.16,17 On the basis of the
optically induced trans–cis isomerization, azo-chromophore
undergoes a macroscopic alignment to the direction of light
polarization. In particular, the surface relief gratings (SRGs)
formation observed for azo-polymer films, which is related to the
mass transport process, is induced by exposure to the appro-
priate optical pattern.18 This facile, erasable, single-step process
allows quick fabrication of large or small area gratings having
small periods, with good control over the grating parameters.
Large amplitude SRGs in thin films of azo polymers with diverse
chemical structures have been successfully written and the
intriguing properties of the gratings continue to be reported.19,20
As the electroactive group is readily covalently linked to the azo-
polymer backbones, the multifunctional copolymers with
photoinduced mass-transport properties can be developed this
way. However, this approach has not yet been extended for
fabricating diffractive gratings in films of multifunctional azo-
copolymers with pendent electroactive groups.
aAlan G. MacDiarmid Institute, College of Chemistry, Jilin University,
Changchun, 130012, P.R. China. E-mail: chaodanming@jlu.edu.cn;
cwang@jlu.edu.cn; Fax: +86-431-85168292; Tel: +86-431-85168292
bDepartment of Chemistry and Materials Science Program, University of
New Hampshire, Durham, NH, 03824, USA
cCollege of Physics, Jilin University, Changchun, 130012, P. R. China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c1jm14047g
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As model compounds of polyaniline (PANI), monodispersed
oligoanilines with well-defined structures have been heavily
investigated due to their good electroactivity, enhanced solubility
and excellent processability.21,22 Recently, considerable effort has
been made in chemically synthesizing polymers based on oli-
goanilines, such as graft, alternating, and star-like polymers.23–25
The introduction of pendent oligoaniline groups into azo-poly-
mer backbones is quite promising as the properties of the
multifunctional copolymers can be tuned reversibly via electro-
chemical modification or light irradiation. As to the pure azo-
polymers, the SRGs can be easily formed in thin films but the DE
of the grafting can’t be modulated with an electrochemical
stimulus, because the azo group has no electroactivity. Similarly,
pure polyaniline can only exhibit the electrochromic property
and can’t be prepared to a patterned film by itself. In this regard,
copolymerization of azo-chromophore and oligoaniline allows
for the single step photofabrication of optical diffraction gratings
based on the azo group and gives rise to a modification of DE
supplied by reversible redox states of oligoaniline responding to
electrochemical modulation. To the best of our knowledge,
research about the formation of electrochemically responsive
SRGs based on electroactive azo polymers is still lacking in the
literature.
multifunctional polyamide with pendant oligoaniline group in
Scheme 1 was prepared by low temperature solution poly-
condensation. The chemical structure of Azo-PA-S-AT was
confirmed by FTIR, 1H NMR spectroscopy and GPC. An FTIR
spectrum of the polyamide showed the characteristic absorption
bonds around 3380 cmꢁ1 corresponding to N–H stretching
vibration, around 2923 cmꢁ1 based on C–H stretching vibration
in methyl groups and around 1658 cmꢁ1 due to C]O stretching
vibration in aryl carbonyl groups. The bond around 1452 cmꢁ1
was attributed to the stretching vibration of N]N and the peak
at 1205 cmꢁ1 could be assigned to the stretching vibration of
1
C–O–C of the aryl ether linkages. The H NMR stacked spec-
trum of Azo-PA-S-AT is shown in Fig. S1.† The protons located
at the electron-rich ortho-ether position were strongly shielded,
and their signals appeared at high-field region (7.34–6.62 ppm),
while the protons located at para- or ortho-positions of carbonyl
groups were deshielded due to their strongly electron-with-
drawing effects, and their signals appeared at low-field region
(8.05–7.85 ppm). The number-average molecular weight (Mn) of
Azo-PA-S-AT was found to be 3.30 ꢂ 104 with a polydispersity
index (Mw/Mn) of 1.62.
The polyamide exhibited outstanding solubility in polar
solvents such as NMP, DMF and DMAc, and the enhanced
solubility could be attributed to the attachment of bulky pendent
groups. Thus, the excellent solubility makes the polymer
a potential candidate for practical applications in spin or dip-
coating processes. The crystallization of Azo-PA-S-AT was
investigated by wide-angle X-ray diffraction pattern and the
result indicates that the polyamide was essentially amorphous,
revealing that the introduction of bulky pendant aniline tetramer
groups disturbed the close packing and regularity of the polymer
chains. The thermal properties of Azo-PA-S-AT were evaluated
by differential scanning calorimetry (DSC) and thermogravi-
metric analysis (TGA). In the DSC curve, the polyamide showed
no clear melting endotherms up to the decomposition tempera-
tures, indicating the amorphous nature of the polyamide. The
glass transition temperature (Tg) of the polyamide was found to
be 158 ꢀC. The TGA trace for this material displayed only
a single step weight loss indicative of backbone decomposition.
The temperature for 10% weight loss of polyamiꢀde in nitrogen
We report herein
a novel multifunctional polyamide
(Azo-PA-S-AT) with pendent aniline tetramer groups synthe-
sized via low temperature solution polycondensation. The elec-
trochromic properties, photo-orientation process and the stable
value of birefringence are presented in detail. We also describe
the preparation of photoinduced SRGs based on the film of
Azo-PA-S-AT and investigated the DE of the fabricated gratings
responding to the electrochemical modulation.
Results and discussion
Characterization and basic properties of Azo-PA-S-AT
The one-step synthetic route for the electroactive diamine
monomer (EDA) is shown in Scheme S1.† The preparation of
EDA was carried out by K2CO3-mediated nucleophilic reaction
and toluene was used to dehydrate the reaction system. The
reaction temperature was first controlled at 140 ꢀC to remove the
water generated during the phenoxide formation, and then
increased slowly to 160 ꢀC to accomplish the reaction. The
ꢀ
was 418 C. The char yield of polyamide at 700 C in nitrogen
was 61 wt%.
Electrochemical activity
The electrochemical behavior of Azo-PA-S-AT was investigated
by cyclic voltammetry (CV) and the results were shown in Fig. 1.
A DMAc solution of the polyamide was cast on the g-c working
electrode and evaporated to form a thin solid film. The CV of the
electrode was performed in 1 mol Lꢁ1 H2SO4 at different
potential scan rates (20–140 mV sꢁ1). The CV of the electrode
underwent two oxidation processes with the oxidation peaks at
370 and 530 mV. The first oxidation peak corresponded to the
transition of leucoemeraldine base (LEB)/emeraldine base (EB),
and the second peak corresponded to the transition of emer-
aldine base (EB)/pernigraniline base (PNB). A linear dependence
of the peak currents as a function of scan rates in the region of
20–140 mV sꢁ1 (inset of Fig. 1) confirmed both a surface
controlled process26 and a well-adhered electroactive polymer
Scheme 1 The synthetic route of the multifunctional polyamide (Azo-
PA-S-AT).
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polyamide thin films changed from a transmissive yellowish
(at ꢁ0.2 V), to green (at ca. 0.4 V), and finally to an absorptive
brown blue (at ca. 0.8 V) (inset of Fig. 2). The above results
indicated that it could be a highly effective method for producing
multicolor electrochromic materials using different concentra-
tions of the two chromophores through copolycondensation.
Electrochromic switching studies were carried out to monitor
changes in the optical contrast at 700 nm during repeated
potential stepping between the neutral (ꢁ0.2 V) and oxidized
state at 0.8 V with a residence time of 60 s. The results for the first
5 cycles were shown in Fig. 3. The optical contrast value (%DT)
was found to be 32% at 700 nm measured between its coloring
(oxidization) and bleaching (reduction) states. Switching time
was the time required to bring the polyamide to its most reduced
state from its most oxidized state or vice versa. It was defined as
the time required for reaching 90% of the full change in the
coloring/bleaching process. The polyamide revealed a switching
time of 2.7 s at 0.8 V for the coloring process at 700 nm and 1.8 s
for bleaching. The coloration efficiency CE (h ¼ DOD/Q) was
a practical tool to measure the power requirements of an elec-
trochromic material. It was measured by monitoring the amount
of ejected charge (Q) as a function of the change in optical
density (DOD) of the polymer film. The electrochromic behavior
of the polyamide exhibited CE up to 128.7 cm2 Cꢁ1 (at 700 nm) at
the first oxidation stage.
Fig. 1 CV of the Azo-PA-S-AT electrode in 1mol Lꢁ1 H2SO4 at different
potential scan rates: 20–140 mV sꢁ1. The inset shows the relationships
between the oxidation peaks and reduction current vs. potential scan rate.
film. The Azo-PA-S-AT film was found to be very stable with
almost no change in its CV diagram after 50 repeated cyclic scans
between 0 and 0.8 V.
Spectroelectrochemistry and electrochromic performances
The electro-optical properties of Azo-PA-S-AT film were inves-
tigated using the changes in absorption spectra under a voltage
pulse. Spectroelectrochemical studies were performed on the film
of polyamide spin-coated on an Indium-Tin Oxide (ITO) glass
slide in 0.01 mol Lꢁ1 H2SO4 couple at applied potentials of ꢁ0.2,
0, 0.2, 0.4, 0.6 and 0.8 V (vs. Ag/AgCl). Fig. 2 presented the
UV-Vis absorption spectra of the polyamide film at various
applied potentials. The peak at 425 nm (related to polarons of
oligoaniline) increased gradually as the potential increased from
ꢁ0.2 to 0.4 V. With an increase in applied potential beyond
0.4 V, the peak decreased as a broad band associated with
superimposed contributions of polaronic and bipolaronic species
of oligoaniline at ꢃ800 nm was introduced.26 The color of the
Photoisomerization of Azo-PA-S-AT
Photoisomerization studies were carried out by irradiating the
DMAc solution and spin-coated thin film, respectively. As
shown in Fig. 4(a), the UV-Vis absorption spectra revealed an
absorption band centered around 333 nm, which was associated
with the overlap of the p–p* transition of the benzoid rings of
oligoaniline and the azobenzene moiety.27 As the irradiation time
increased, the intensity of the absorption decreased and the
absorption band underwent a blue shift, due to a trans-to-cis
photoisomerization process of the azobenzene chromophore.
The blue shift might be induced by the decrease in the extent of
p-conjugation due to the photoisomerization.28 On the other
Fig. 2 The spectral changes of an Azo-PA-S-AT/ITO electrode (0.6 ꢂ
3 cm2) in 0.01 mol Lꢁ1 H2SO4 at different potentials. The inset shows
photographs of the Azo-PA-S-AT/ITO electrode at different potentials.
Fig. 3 (a) Current consumption and (b) absorbance changes monitored
at 700 nm of an Azo-PA-S-AT/ITO electrode in 0.01mol Lꢁ1 H2SO4 for
the first 5 cycles.
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Fig. 4 Changes in the UV-Vis absorption spectra of Azo-PA-S-AT with different irradiation times: (a) and (b) in DMAc solution, (c) and (d) as spin-
coated films.
hand, when the solution was irradiated with visible light, the
absorption peak at 333 nm (Fig. 4(b)) will gradually recover to its
initial value prior to irradiation. We also conducted this process
on a spin-coated thin film, and the results in Fig. 4(c) and (d)
exhibited a similar reversibility to those in solution. Compared
with the spectra of the polyamide in DMAc solution, the lmax for
the thin film red-shifted to 340 nm, which might be caused by
a solvatochromic effect of the azo chromophores.29 Besides, the
time to reach a photostationary state for the solid film was
shorter than that in solution. It was related to the relative lower
concentration of the polymer in the film.
conserved after relaxation declined a little with the remaining
birefringence larger than 96% of the initial value, indicating that
the polyamide presented improved stability in the case of the
photoinduced orientation. This was mainly attributed to the high
glass transition temperature and rigid aromatic structure of the
polyamide which limited the relaxation process of the oriented
chromophore groups.34 Finally, the azo-chromophore orienta-
tion was completely randomized after circularly polarized light
was introduced (point C). Moreover, the maximum and satu-
rated value of the photo-induced birefringence changed slightly
after several cycles.
Patterning of Azo-PA-S-AT thin films
Photoinduced birefringence
In past years, lots of work has focused on approaches to produce
micropatterned films of electroactive polymers.35,36 However,
Optical storage experiments were carried out using a pump beam
(532 nm of Nd:YAG laser) with a polarization angle of 45ꢀ with
respect to the polarization direction of a low-power laser oper-
ating at 850 nm (reading beam). The wavelength of the probe
light was just outside the absorption band of the film of Azo-PA-
S-AT in LEB form. The experimental set-up was similar to that
previously reported.30
A typical multiple writing–erasing curve of the polyamide film
was presented in Fig. 5. Before irradiation, no optical anisotropy
was observed because of the random orientation of the azo
chromophore. As the polarized Nd:YAG laser beam radiation
was introduced (point A), an anisotropic orientation distribution
was expected immediately as a consequence of the alignment of
the azo chromophore changing on account of the trans–cis–trans
isomerization of the azo moiety. While the writing beam was
turned off at point B, the birefringence value exhibited a little
decay and then reached a stable state in a few minutes. It was
mainly caused by thermally activated dipole reorientation which
would tend towards randomization of the anisotropy.31
Compared with other azo-polymers,32,33 the birefringence
Fig. 5 Multiple ‘writing–erasing’ photoinduced birefringence on Azo-
PA-S-AT film (d ¼ 4 mm) at room temperature.
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multistep
photolithographic
techniques
and
electro-
electrochemical modulation of the DE for the grating-patterned
polyamide film was shown in Fig. 7. The SRGs were supported
on an ITO electrode and subjected to potential cycling (ꢁ0.2 to
1.0 V), while the intensities of the transmitted and first-order
diffracted beams from a 633 nm He–Ne laser were monitored. As
can be seen, these electrochemically-induced changes in DE
could be reversibly switched many times, and the signal was
lagging behind the potential variation. Between ꢁ0.2 and 0.2 V,
the DE remained constant when the polyamide was reduced to
the LEB form. Interestingly, as the potential increased from 0.2
to 0.7 V, the DE decreased while the polyamide gratings changed
from LEB to EB, then to PNB. With the potential increased
beyond 0.7 V, the DE changed slightly because the polyamide
was totally oxidized to the PNB form without any influence on its
structure. This was in accordance with the change of n of poly-
aniline following the potential variation,41,42 as the DE was
considerably more sensitive to changes in n than to changes in
absorptivity.43 The origin of the redox-induced modulation in the
DE was predominated by the change of n, which was coupled
with the oligoaniline oxidation/reduction. In addition, the signal
lagging behind the potential variation is about 25 s. However, the
hysteresis was not observed in the spectroelectrochemical
measurements. This phenomenon could be explained possibly as
follows. First of all, during the SRG formation process, the
photoinduced alignment of polymer chains and large-scale
polymerization steps are commonly required for the fabrication
of patterned electroactive polymer films. Recently, the developed
photofabrication process of surface relief gratings (SRGs) has
offered for a quick formation of diffraction gratings with desired
periods.37 On the other hand, oligoaniline with well-defined
structure shows reversible redox properties during the electro-
chemical switching. So we can take advantages of single step
photofabrication of patterned films based on the azo group and
various redox states of oligoainile responding to electrochemical
modulation to prepare electrochemically responsive diffraction
gratings.
A typical experimental setup used for the photofabrication of
SRGs has been reported.19 Exposing Azo-PA-S-AT film to two
interfering linearly p-polarized beams (Nd:YAG laser, 355 nm)
formed the surface-relief gratings. It is a good way to increase
storage capacity using a shorter wavelength of light as demon-
strated by the new BluRay technology. SRGs of the polyamide
could be rapidly fabricated within 20 s at room temperature at an
intensity of 80 mW cmꢁ2. After forming the SRGs, the exposed
region is scanned with an Atomic Force Microscope (AFM,
Nanoscope III, Digital Instruments) in tapping mode. Fig. 6
showed a representative region of the surface of patterned film.
The gratings revealed a well-shaped micropattern with an
amplitude modulation of 147 nm. The spatial period was equal to
the period of the interference pattern of 1.4 mm, depending on
both the angle between the two interfering beams and the
wavelength of the writing beam.
Electrochemically modulated optical diffraction gratings
The diffraction efficiency (DE) of a grating depends on the
optical properties (the absorptivity k and the refractive index n)
of a grating material.38 It is well-known that oligoaniline exhibits
a change in absorptivity (k) concomitant with a change in redox
state during electrochemical switching due to the electrochromic
effect. At the same time, the refractive index (n) of oligoaniline
will also change with the redox states due to the close relationship
between the absorptivity (k) and the refractive index (n)
according to the Kramers–Kronig relation.39 By making use of
this effect and employing the SRGs formation process described
above, we have fabricated optical diffraction gratings with which
the DE can be modulated by an electrochemical signal.
The apparatus used for DE measurements is similar to the
previous literature.40 The experimental example of the
Fig. 7 Diffraction efficiency changes with the potential change of Azo-
PA-S-AT diffraction gratings at a sweep rate of 10 mV sꢁ1
.
Fig. 6 AFM images of a patterned Azo-PA-S-AT film, (a) the plane view of the SRGs (10 ꢂ 10 mm2), (b) a typical 3-D view of the SRGs.
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macromolecular motion lead to a change in the microstructure of
the films. Consequently, the conductivity of the film will also
change, which gives rise to an obvious hysteresis. Another
contributory factor is the much thicker thickness of the film for
SRGs. As a result, it will spend more time completing the
exchange of the neutral molecular and ion between the solution
and the film, which is an essential process of redox cycling.
Differential scanning calorimeter (DSC) measurements were
performed on a Mettler Toledo DSC821e instrument. A Perkin-
Elmer PYRIS 1 TGA was used to investigate the thermal
stability of the polymer. The CV was investigated on a CHI
660c Electrochemical Workstation (CH Instruments, USA)
with a conventional three-electrode cell, using an Ag/AgCl cell
as the reference electrode, a platinum wire electrode as the
counter electrode, and a glassy carbon electrode (F3.0 mm) as
the working electrode. Spectroelectrochemical measurements
were carried out in a cell built from a 1 cm commercial cuvette
using a UV-2501 PC Spectrometer (SHIMADZU). The ITO-
coated glass was used as the working electrode, a Pt wire as the
counter electrode, an Ag/AgCl cell as the reference electrode
and 0.01 mol Lꢁ1 H2SO4 as the electrolyte. Photoisomerization
of Azo-PA-S-AT was conducted using a high pressure mercury
Conclusions
Well-defined oligoaniline-containing azo-polyamide prepared by
low temperature solution polycondensation exhibits high Tg,
good thermal stability and reversible electrochemical properties.
The obtained polyamide reveals valuable electrochromic char-
acteristics with a high contrast value, low switching times and
moderate coloration efficiency. The polyamide presents high
stability of the induced order (96% of photoinduced birefrin-
gence is maintained after relaxation) upon irradiation. Utiliza-
tion of the one-step photofabrication of SRGs as
electrochemically responsive diffraction gratings was demon-
strated. This single step approach offers an opportunity to
fabricate patterns in electroactive azo polymer films. The elec-
trochemically induced changes in diffraction efficiency are in
accord with the change in the refractive index that occurs
concomitant with a change in the redox state of the oligoaniline.
This multifunctional polyamide, bearing distinct functional
groups, will be of potential interest, since it is suitable for smart
windows, optical switches, reversible high density optical storage
and diffraction-based sensing devices.
lamp in conjunction with a band-pass UV filter (lmax
¼
360 nm). UV-Vis spectra were recorded on a UV-2501 PC
Spectrometer.
Synthesis of electroactive diamine monomer (EDA)
The synthetic routes for the preparations of compound 1 and
EDA are depicted in Scheme S1.† We have reported the suitable
preparation of EDA in the literature.44
MALDI-TOF-MS: m/z calculated for C43H36N6O3 ¼ 684.78.
Found 685.0. FTIR (KBr, cmꢁ1): 3380 (s, yNH), 3037 (m, yCH),
1657 (vs, yC]O), 1602 (s, yC]C of benzenoid rings), 1506 (vs, yC]C
of benzenoid rings), 1294 (s, yC–N), 1233 (m, yC–O–C), 829 (m,
1
dCH), 750 (m, dCH), 696 (m, dCH). H NMR (d6-DMSO, ppm):
d ¼ 10.24 (s, 1H, due to H1), d ¼ 7.74 (s, 1H, due to H4), d ¼ 7.69
(s, 1H, due to H3), d ¼ 7.60 (s, 1H, due to H2), d ¼ 7.54 (d, 2H, due
to H7), d ¼ 7.14 (t, 3H, due to H6, H9), d ¼ 6.93 (d, 12H, due
to H10), d ¼ 6.81 (d, 4H, due to H13), d ¼ 6.67 (t, 1H, due to H5),
d ¼ 6.59 (d, 4H, due to H12), d ¼ 6.29 (d, 2H, due to H8), d ¼ 4.99
(s, 4H, due to H11).
Experimental
Materials
All chemicals, including 3-methyl-4-nitrobenzoic acid, sodium
hydroxide, glucose, acetic acid, thionyl chloride, 4-aminophenol
and anhydrous lithium chloride, were purchased from Shanghai
Chemical Factory. DMAc and toluene were used as received
without further purification. Distilled water was self-made.
Anhydrous potassium carbonate was dried at 110 ꢀC for 24 h
before use. Optically transparent ITO glass substrates (Reintech
electronic technologies CO., 10 U/square) with dimensions of
6.0 ꢂ 0.6 cm2 were used as thin film electrodes.
Synthesis of trans-azobenzene-4,40-dicarbonyl chloride
(compound 3)
12 g 3-menthyl-4-nitrobenzoic acid (66.2 mmol) and sodium
hydroxide (40 g, 1 mol) were dissolved in 250 mL water and the
solution was kept at 50 ꢀC. A solution of glucose (80 g,
444 mmol) in 120 mL water was added dropwise in 40 min to the
above solution with stirring at 50 ꢀC. The reaction was main-
Measurements
ꢀ
tained at 50 C in the air for 16 h. After cooling down to room
Mass spectrometry (MS) was performed on an AXIMA-CFR
laser desorption ionization time of flight spectrometer
(COMPACT). Fourier-transform infrared spectra (FTIR)
measurements were recorded on a BRUKER VECTOR 22
spectrometer. The nuclear magnetic resonance spectra (NMR)
were run on a BRUKER-500 spectrometer. The number-
average molecular weight (Mn), weight-average molecular
weight (Mw), and molecular weight distribution of the polymer
were measured with a gel permeation chromatography (GPC)
instrument equipped with a Shimadzu GPC-802D gel column
and SPD-M10AVP detector with DMF as an eluent at a flow
rate of 1 mL minꢁ1. Wide-angle X-ray diffraction (WAXD)
measurements were made using a Siemens D5005 diffractometer
equipped with a Cu-Ka radiation source at room temperature.
temperature, the mixture was adjusted to pH 6 with glacial acetic
acid and the precipitate was collected by filtration. Then it was
purified by recrystallization with hot K2CO3 solution.
2.98 g compound 2 (10 mmol), 60 mL thionyl ꢀchloride, and few
drops of DMF were combined in a flask at 90 C for 10 h. Thi-
onyl chloride was removed from the solution by simple distilla-
tion. The residue was purified by reduced pressure distillation to
afford trans-azobenzene-4,40-dicarbonyl chloride 2.64 g (yield:
88%).
MALDI-TOF-MS: m/z calculated for C16H12Cl2N2O2
¼
335.18. Found 335. FTIR (KBr, cmꢁ1): 3081 (m, yC–H of benze-
noid rings), 2972 (m, yC–H of methyl groups), 1763 (vs, yC]O),
1747 (s, yC]O), 1593 (m, yC]C of benzenoid rings), 1421 (m,
1
yN]N), 822 (m, dCH), 760 (w, dCH), 686 (m, dCH). H NMR
18322 | J. Mater. Chem., 2011, 21, 18317–18324
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(CDCl3, ppm): d ¼ 8.13 (s, 2H, due to Hd), d ¼ 8.02 (dd, 2H, due
to Ha), d ¼ 7.66 (d, 2H, due to Hb), d ¼ 2.81 (s, 6H, due to Hc).
performed in a quartz cuvette using a CHI 660c Electrochemical
Workstation, with a Pt wire used as the counter electrode, an
Ag/AgCl cell as the reference electrode and 0.01 mol Lꢁ1 H2SO4
as the electrolyte. To characterize a grating, a probe beam of
He–Ne laser beam (632.8 nm) was passed through an aperture
that made the beam diameter adjustable and then perpendicu-
larly irradiated on the grating. The zero-order and first-order
diffraction beams were collected with silicon photodiodes which
are fixed on the optical stages for fine adjustment of the positions.
The DE of the gratings was calculated as the ratio of I1/I0, where
I0 and I1 were the intensities of incident light and light in the 1st
diffraction order, respectively.
Synthesis of the multifunctional polyamide (Azo-PA-S-AT)
A solution of 2.738 g (4 mmol) EDA in 30 mL DMAc was added
dropwise over a period of 2 h to a stirred mixture of compound
3 (1.2735 g, 3.8 mmol) and anhydrous lithium chloride (0.3545 g,
6 mmol) in 100 mL DMAc. The reaction was carried out in an ice
bath with a nitrogen flow. Following the addition of the solution
of EDA, the resulting mixture was stirred for 4 h and then poured
into water. The product, filtered from the mixture, was subse-
quently washed with water three times and acetone once, filtered
and dried in a vacuum oven at 50 ꢀC for 24 h. The brown powder
was obtained in 87% yield.
Acknowledgements
FTIR (KBr, cmꢁ1): 3380(m, yNH), 3029 (w, yC–H of benzenoid
rings), 2923 (m, yC–H of methyl groups), 2854 (w, yC–H of methyl
groups), 1658 (m, yC]O), 1602(s, yC]C of benzenoid rings), 1504
(vs, yC]C of benzenoid rings), 1452 (m, yN]N), 1301 (s, yC–N),
This work has been supported in part by the National Natural
Science Foundation of China (No. 21104024 and 50973038), and
the National 973 Project (No. S2009061009).
1
1205 (m, yC–O–C), 821 (m, dCH), 748 (m, dCH), 696 (m, dCH). H
Notes and references
NMR (d6-DMSO, ppm): d ¼ 10.44 (due to H1), d ¼ 10.34 (due to
H2), d ¼ 8.05–7.85 (due to H13–15), d ¼ 7.70–7.53 (due to H3–5),
d ¼ 7.34–6.62 (due to H6–12), d ¼ 2.78 (due to H16). GPC:
number-average molecular weight (Mn) 3.30 ꢂ 104; poly-
dispersity (Mw/Mn) 1.62.
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