Enhanced near-infrared electrochromism in triphenylamine-based aramids bearing phenothiazine redox centers

Article abstract of DOI:10.1039/c0jm01889a

A series of organosoluble polyamides based on N-phenothiazinylphenyl redox units showing anodically electrochromic characteristics both in the near-infrared (NIR) and visible light regions were prepared from the phosphorylation polyamidation reactions of

Full text of DOI:10.1039/c0jm01889a

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Enhanced near-infrared electrochromism in triphenylamine-based aramids
bearing phenothiazine redox centers†
*
Hung-Ju Yen and Guey-Sheng Liou
Received 14th June 2010, Accepted 27th July 2010
DOI: 10.1039/c0jm01889a
A series of organosoluble polyamides based on N-phenothiazinylphenyl redox units showing
anodically electrochromic characteristics both in the near-infrared (NIR) and visible light regions were
prepared from the phosphorylation polyamidation reactions of a newly synthesized diamine monomer,
4,40-diamino-400-N-phenothiazinyltriphenylamine, with various dicarboxylic acids. These polymers
were readily soluble in many polar solvents and showed useful levels of thermal stability associated with
relatively high glass-transition temperatures (Tg) (255–277 ꢀC) and high char yields (higher than 67% at
800 ꢀC in nitrogen). In addition, the polymer films showed reversible electrochemical oxidation with
enhanced NIR contrast, high coloration efficiency (CE), low switching time, and anodic green/purple
electrochromic behaviors.
for NIR applications due to its particular structure and electron
Introduction
transfer in the oxidized states.
Electrochromic materials reveal reversible optical changes in
absorption or transmittance upon electrochemically oxidized or
reduced, such as transition-metal oxides, inorganic coordination
complexes, conjugated polymers, and organic molecules.1
Initially, investigation of electrochromic materials directed
towards optical changes in the visible region (e.g., 400–800 nm),
proved useful and variable applications such as E-paper, optical
switching devices, smart window, and camouflage materials.2
Increasingly, attention of the optical changes has been focused
on extending from the near infrared (NIR; e.g., 800–2000 nm)
through to the microwave regions of the spectrum, which could
be exploitable for optical communication, data storage, and
thermal control (heat gain or loss) in buildings and spacecraft.3
Therefore, NIR electrochromic materials including transition
metal oxides (WO3), organic metal complex (ruthenium den-
drimer), and quinone-containing organic materials have been
investigated in recent years.4 Wang and Wan made efforts on the
quinone-containing electrochromic materials, which revealed
high absorption in the NIR upon electrochemical reduction.4c–4g
Reynolds’ group reported color-to-transmissive NIR electro-
chromic conjugated polymers and their device, exhibited multi-
colors in the neutral state and transmissive in the oxidized state.5a
In addition to conjugated polymers,5 the phenothiazine-con-
taining molecule is an interesting anodic electrochromic system
Phenothiazine (10H-dibenzo-[b,e]-1,4-thiazine; PSN) is a well-
known heterocyclic compound with electron-rich sulfur and
nitrogen heteroatoms. Organic molecules6 and polymers7 con-
taining phenothiazine reversible redox units have recently
attracted much research interest because of their unique electro-
optical properties and resulting potential in diverse applications
such as light-emitting diodes,6a,7b,7c photovoltaic devices,6c,7d and
chemiluminescence.7a Interestingly, the intermolecular/intra-
molecular electron transfer between bridged PSN centers in the
mixed-valence cation radicals state leading to the absorption
bands in the NIR region, was delineated by Kochi.8 Moreover,
the absorbance of its dications also appeared in the NIR (800–
1200 nm) range due to the nearly coplanar structure of PSN
redox centers (q ¼ 172ꢀ), indicating a great potential in anodic
electrochromic systems for NIR applications.
Triarylamine derivatives are well known as its photo- and
electroactive properties have potential for optoelectronic appli-
cations, such as photoconductors, hole-transporters, light-emit-
ters, and memory devices.9 Electron-rich triarylamines can be
easily oxidized to form stable radical cations, and the oxidation
process is always associated with a noticeable change of colora-
tion. Thus, studies of the synthesis and electrochromism of tri-
arylamine-based polymers have been reported in the literature.10
Since 2005, our groups have initiated some high-performance
polymers (e.g., aromatic polyamides and polyimides) bearing the
triarylamine unit as an electrochromic functional moiety.11 It has
also been reported in our previous publications12 that the
incorporation of electron-donating substituents such as methoxy
and tert-butyl groups at the para-position of phenyl groups on
the electrochemically active sites of the triphenylamine (TPA)
unit resulted in stable TPA cationic radicals and decreased
oxidation potential, leading to a significantly enhanced redox
and electrochromic stability of the prepared polyamides.
In this article, we therefore synthesized the novel PSN-TPA-
based monomer, 4,40-diamino-400-N-phenothiazinyltriphenyl-
amine (4), and its derived polyamides containing electroactive
Functional Polymeric Materials Laboratory, Institute of Polymer Science
and Engineering, National Taiwan University, 1 Roosevelt Road, 4th Sec.,
Taipei, 10617, Taiwan. E-mail: gsliou@ntu.edu.tw
† Electronic supplementary information (ESI) available: Detailed
experiments and characterizations of monomers were described.
Inherent viscosity, molecular weights, solubility behavior, and thermal
properties of polyamides, and electrochemical properties of model
compounds are provided in Tables. Figures showing NMR spectra of
3, 4, and Ib. IR, TGA, TMA curves, UV-visible transmission spectra,
electrochemical properties of polyamides, and electrochemical
properties of model compounds are provided. See DOI:
10.1039/c0jm01889a
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TPA groups with para-substituted phenothiazinyl moieties which
could not only greatly prevent the electrochemical coupling
reactions by affording stable cationic radicals but also enhance
the NIR absorption during oxidative procedure. It is well known
that the aromatic polyamides as microelectronic materials have
attracted great interest due to their outstanding thermal and
mechanical resistance.13 Incorporation of packing-disruptive
TPA and PSN units into polyamides not only preserves high
thermal stability, glass transition temperature, and solubility for
enhancing film-forming ability which is beneficial for their
fabrication of large-area, thin-film electrochromic devices but
also provides the electroactive center to facilitate both processing
and electrochromic applications. We anticipated that the
prepared polyamides should be stable for multiple electro-
chromic switching, improving optical response times, and
enhancing CE with high NIR contrast. For a comparative study,
electrochemical and electrochromic properties of the present
polyamides were also compared with that of structurally related
ones from N,N-bis(4-aminophenyl)-N0,N0-diphenyl-1,4-phenyl-
enediamine (40) that has been reported previously.11
4-fluoronitrobenzene in the presence of caesium fluoride.
Elemental analysis, FAB-MS, IR, and NMR spectroscopic
techniques were used to identify structures of the intermediate
compounds 1–3, and the target diamine monomer 4. Fig. S1 and
S2 (ESI†) illustrate the H NMR and 13C NMR spectra of the
1
dinitro compound 3 and diamine monomer 4, respectively.
Assignments of each carbon and proton are assisted by the two-
dimensional NMR spectra shown in Fig. S3 and S4,† and these
spectra agree well with the proposed molecular structure.
Polymer synthesis
According to the phosphorylation technique first described by
Yamazaki,14 a series of novel polyamides I with pendent N-
phenothiazinylphenyl units were synthesized from the diamine
monomer 4 with various dicarboxylic acids 5a–5d (Scheme 2).
The polymerization was carried out via solution poly-
condensation using triphenyl phosphite and pyridine as
condensing agents. All polymerization reactions proceeded
smoothly and gave high molecular weights. The obtained poly-
amides had inherent viscosities in the range of 0.29–0.36 dL/g
with weight-average molecular weights (Mw) and degree of
polymerization (DP) in the range of 38500–160900 daltons and
42–114, respectively, relative to polystyrene standards
(Table S1†). All the polymers could afford transparent and tough
films via solution casting, indicating high molecular weights.
The structures of polyamides were confirmed with IR and
NMR spectroscopy. A typical FT-IR spectrum for polyamide Ic
is given in Fig. S5.† The characteristic IR absorption bands of the
amide group appeared at 3304 (N–H stretch) and 1654 cmꢁ1
(amide carbonyl). 1H NMR and 13C NMR spectra of polyamide
Ib are illustrated in Fig. S6.† Assignments of each carbon
and proton are given in the figure and assisted by the
Results and discussion
Monomer synthesis
N-(4-Aminophenyl)phenothiazine (2) was prepared by the CsF-
mediated, aromatic fluoro-displacement reaction of phenothia-
zine with 4-fluoronitrobenzene followed by hydrazine Pd/C-
catalytic reduction according to the synthetic route outlined in
Scheme 1. The new aromatic diamine having a bulky pendent N-
phenothiazine
group,
4,40-diamino-400-N-phenothiazinyl-
triphenylamine (4), was successfully synthesized by hydrazine
Pd/C-catalyzed reduction of the dinitro compound 3 resulting
from double N-arylation reaction of compound
2 with
Scheme 1 Synthetic route to diamine monomer 4.
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Scheme 2 Synthesis of aromatic polyamides Ia–Id. The photograph shows appearance of the polyamide films (thickness ꢂ3 mm).
two-dimensional C–H HMQC NMR spectra (Fig. S7†), and
these spectra agree well with the proposed polymer structure. A
structurally related polyamide I0c derived from diamine 40 is used
for comparison studies. The synthesis and characterization of
polymer I0c has been described previously.11b
in both air and nitrogen atmospheres are shown in Fig. S9.† All
the prepared polyamides exhibited good thermal stability
without significant weight loss up to 400 ꢀC in nitrogen. The 10%
weight-loss temperatures (Td10) of these polymers in nitrogen and
air were recorded in the range of 500–585 and 485–570 ꢀC,
respectively. The carbonized residue (char yield) of these poly-
mers in a nitrogen atmosphere was more than 67% at 800 ꢀC. The
high char yields of these polymers can be ascribed to their high
aromatic content. The glass-transition temperatures (Tg) of these
polymers could be easily measured in the DSC thermograms;
they were observed in the range of 255–277 ꢀC, depending upon
the stiffness of the polymer chain. All the polymers indicated no
clear melting endotherms up to the decomposition temperatures
on the DSC thermograms, which supports the amorphous nature
of these polyamides. The softening temperatures (Ts) (may be
referred as apparent Tg) of the polymer film samples were
determined by the TMA method with a loaded penetration
probe. They were obtained from the onset temperature of the
probe displacement on the TMA traces. A typical TMA ther-
mogram for polymer Ia is illustrated in Fig. S10.† In most cases,
the Ts values obtained by TMA are comparable to the Tg values
measured by the DSC experiments.
Solubility and film property
The solubility behavior of aromatic–aliphatic polyamide Ia and
aromatic polyamides Ib–Id was tested qualitatively, and the
results are presented in Table S2.† All the polymers were readily
soluble in polar aprotic organic solvent such as NMP, DMAc,
DMF, and m-cresol. Thus, the excellent solubility makes these
polymers potential candidates for practical applications by spin-
coating or inkjet-printing processes to afford high performance
thin films for optoelectronic devices. As shown in Scheme 2, the
cast films are transparent (for Ia, Ic and Id) and light yellowish
green (for Ib) in color. Their high solubility and amorphous
properties can be attributed to the incorporation of a bulky
pendent N-phenothiazinyl group to the para-position of TPA
backbone, which results in a high steric hindrance to close
packing, and thus reduces their crystallization tendency. The
cutoff wavelengths (absorption edge; l0) from UV-vis trans-
mittance spectra were in the range of 366–424 nm (Fig. S8†). Due
to a lower capability of charge transfer, the polyamide Ia film
showed an almost colorless and highly optical transparency with
a cutoff wavelength at 366 nm.
Electrochemical properties
The redox behavior of the polyamides were investigated by cyclic
voltammetry (CV) conducted for the cast film on an ITO-coated
glass substrate as working electrode in anhydrous CH3CN and
DMF containing 0.1 M of TBAP as an electrolyte under nitrogen
atmosphere for oxidation and reduction measurements, respec-
tively. Fig. 1 and Fig. S11† display the typical CV of Ic, which
undergoes two reversible oxidation and one reduction processes.
During the electrochemical oxidation of the polyamide thin
Thermal properties
The thermal properties of polyamides were examined by TGA,
TMA, and DSC, and the thermal behavior data are summarized
in Table S3.† Typical TGA curves of representative polyamide Ic
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agreement with 1,4-bis(N-phenothiazinyl)benzene,8 emphasizing
the less electronic coupling interaction between para-phenylene-
bridged redox centers than that in tetraphenyl-p-phenylenedi-
amine-based polyamide I0c. The redox potentials of the
polyamides and their respective highest occupied molecular
orbital (HOMO) and lowest unoccupied molecular orbital
(LUMO) (on the basis that the external ferrocene/ferrocenium
redox standard is 4.8 eV below the vacuum level with
Eonset ¼ 0.36 V)15 estimated from the onset of their oxidation in
CV experiments are summarized in Table 1.
Spectroelectrochemistry
Spectroelectrochemical experiments were used to evaluate the
optical properties of the electrochromic films. For the investi-
gations, the polyamide film was cast on an ITO-coated glass
slide, and a homemade electrochemical cell was built from
a commercial ultraviolet (UV)-visible cuvette. The cell was
placed in the optical path of the sample light beam in a UV-vis-
NIR spectrophotometer, which allowed us to acquire electronic
absorption spectra under potential control in a 0.1 M TBAP/
MeCN solution. UV-vis-NIR absorbance curves correlated to
applied potentials and three-dimensional transmittance-wave-
length-applied potential correlation of Ic film were depicted in
Fig. 2.
Fig. 1 Cyclic voltammograms of polyamide Ic and I0c films on an ITO-
coated glass substrate and ferrocene (inset) in 0.1 M TBAP/CH3CN at
scan rate of 50 mV sꢁ1
.
films, the color of the film changed from colorless to green and
then to deep purple. The other polyamides showed similar CV
curves to that of Ic. Fig. S12 and Table S4† show the electro-
chemical behaviour of M1, M2, and M3, which revealed oxida-
tion processes at Eonset ¼ 0.73, 0.75, and 0.96, respectively.
Contrary to polyamide I0c, the first (E1/2 ¼ 0.75 V) and second
(E1/2 ¼ 1.00 V) oxidation processes for polyamide Ic could be
attributed to successive one electron removal from the pheno-
thiazine and TPA units. Therefore, based on the CV studies of
model compounds, we proposed the possible oxidative order of
the nitrogen atoms for polyamide Ic and I0c in Scheme 3. The CV
curve of polyamide Ic with higher oxidative potential was also in
In the neutral form (0 V), the film exhibited strong absorption
at around 333 nm, characteristic for triarylamine, but it was
almost colorless in the visible region. Upon oxidation (increasing
applied voltage from 0 to 1.05 V), the intensity of the absorption
peak at 333 nm gradually decreased while a new peak at 405 nm
and a broad band having its maximum absorption wavelength at
Scheme 3 The oxidation pathway of polyamide Ic and I0c.
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Table 1 Redox potentials and energy levels of polyamides
Thin films/nm
Oxidation/Va
Reduction/Vb
c
E1/2
EgEC/eVd
EgOpt/eVe
HOMO/eVf
LUMO/eV
c
Index
lmax
lonset
1st
2nd
Eonset
E1/2
Eonset
Ia
Ib
Ic
326
333
333
333
342
370
426
395
403
393
0.72
0.73
0.75
0.72
0.64
0.95
1.00
1.00
1.01
0.95
0.61
0.61
0.66
0.64
0.54
ꢁ1.84
ꢁ1.97
ꢁ1.82
ꢁ1.92
ꢁ2.00
ꢁ2.07
ꢁ1.94
ꢁ2.04
2.61
2.68
2.60
2.68
3.35
2.91
3.16
3.08
3.16
5.05
5.05
5.10
5.08
4.98
2.44
2.37
2.50
2.40
1.82
Id
I0cg
a
From cyclic votammograms versus Ag/AgCl in CH3CN. b From cyclic votammograms versus Ag/AgCl in DMF. c E1/2: Average potential of the redox
couple peaks. d Difference between the two Eonset calculated from oxidation and reduction redox couples. e The data were calculated from polymer films
by the equation: Eg ¼ 1240/lonset (energy gap between HOMO and LUMO). f The HOMO energy levels were calculated from cyclic voltammetry and
were referenced to ferrocene (4.8 eV; onset ¼ 0.36 V). g Data of structurally similar polyamide I0c having the corresponding dicarboxylic acid residue as
in polyamide Ic.
Fig. 2 Electrochromic behavior (left) at applied potentials of (a) 0.00, (b) 0.70, (c) 0.75, (d) 0.80, (e) 0.85, (f) 0.90, (g) 1.00, (h) 1.05, (i) 1.10, (j) 1.15, (k)
1.20, (l) 1.30 (V vs. Ag/AgCl), and 3-D spectroelectrochemical behavior (right) from 0.00 to 1.30 (V vs. Ag/AgCl) of polyamide Ic thin film (ꢂ70 nm in
thickness) on the ITO-coated glass substrate in 0.1 M TBAP/CH3CN.
970 nm in the NIR region gradually increased in intensity. We
attribute the spectral change to the formation of a stable mon-
ocation radical of the PSN moiety, which was consistent with the
phenomenon classified by Kochi.8 As the more anodic potential
to 1.30 V, the absorption peaks at 405 nm and 533 nm further
increased with a new broad band centered at around 865 nm,
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Fig. 3 Electrochromic behavior of polyamide Ic and I0c thin films on the ITO-coated glass substrate in 0.1 M TBAP/CH3CN as their neutral, cation,
and dication forms.
corresponding to the dication form. Notably, the absorption
contrast in the NIR range was enhanced because of the oxidized
PSN unit having a more extended conjugation length than TPA
(Scheme 3), which resulted in a bathochromic shift when
compared with TPA-based polyamide I0c as shown in Fig. 3. The
observed UV-vis-NIR absorption changes in the polyamide Ic
film at various potentials are fully reversible and are associated
with strong color changes. The other polyamides showed
a similar spectral change to that of Ic. From the inset shown in
Fig. 2, the polyamide Ic film switches from a transmissive neutral
state (colorless; Y: 85; x, 0.313; y, 0.330) to a highly absorbing
semi-oxidized state (green; Y: 26; x, 0.352; y, 0.472) and a fully
oxidized state (deep purple; Y; 7; x, 0.345; y, 0.317). The film
colorations are distributed homogeneously across the polymer
film and survive for more than hundreds of redox cycles. The
polymer Ic shows a good contrast both in the visible and NIR
regions with an extremely high optical transmittance change
(D%T) of 54% at 405 nm and 60% at 970 nm for green coloring at
the first oxidation stage, and 81% at 865 nm for purple coloring
Fig. 4 Calculation of optical switching time at (a) 970 nm and (b)
at the second oxidation stage, respectively.
current–time curves of polyamide Ic thin film (ꢂ70 nm in thickness) on
the ITO-coated glass substrate (coated area: 1.2 cm ꢃ 0.5 cm) in 0.1 M
Electrochromic switching
TBAP/CH3CN.
For electrochromic switching studies, polymer films were cast on
ITO-coated glass slides in the same manner as described above,
and chronoamperometric and absorbance measurements were
performed. While the films were switched, the absorbance at the
given wavelength was monitored as a function of time with UV-
vis-NIR spectroscopy. The switching time of polyamide Ic shown
in Fig. 4 was calculated at 90% of the full switch because it is
difficult to perceive any further color change with the naked eye
beyond this point. As depicted in Fig. 4(a), polyamide Ic thin film
revealed a switching time of 5.65 s at 0.87 V for the coloring
process at 970 nm and 0.98 s for bleaching. The amounts of Q
were calculated by integration of the current density and time
obtained from Fig. 4(b) as 1.718 mC cmꢁ2 and 1.632 mC cmꢁ2 for
the oxidation and reduction processes at the first oxidation stage,
respectively. The ratio of the charge density was 95.0%, indi-
cating that charge injection/extraction was reversible during the
electrochemical reactions. The electrochromic stability of the
polyamide Ic film was determined by measuring the optical
change as a function of the number of switching cycles shown in
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coloration efficiency, and high-level electrochromic/electroactive
reversibility. Thus, these characteristics indicate the incorpora-
tion of pendent PSN groups is a new approach for tuning the
coloration change and the prepared polyamides have great
potential for applications in both the NIR and visible regions.
Experimental
Materials
N-phenylphenothiazine16 (M1), and 4,40-Bis(4-benzoylamino)-
triphenylamine12d (M2), were synthesized according to previ-
ously reported procedures. Commercially available dicarboxylic
acids such as trans-1,4-cyclohexanedicarboxylic acid (5a), ter-
ephthalic acid (5b), 4,40-oxydibenzoic acid (5c), and 2,20-bis(4-
carboxyphenyl)hexafluoropropane (5d) were purchased from
TCI and used as received. Commercially obtained anhydrous
calcium chloride (CaCl2) was dried under vacuum at 180 ꢀC for 8
h. Tetrabutylammonium perchlorate (TBAP) (Acros) was
recrystallized twice by ethyl acetate under a nitrogen atmosphere
and then dried in vacuo prior to use. All other reagents were used
as received from commercial sources.
Fig. 5 (a) Current consumption and (b) electrochromic switching
between 0 and 0.87 V (vs. Ag/AgCl) and absorbance change monitored at
405 nm and 970 nm of polyamide Ic thin film (ꢂ70 nm in thickness) on
the ITO-coated glass substrate (coated area: 1.2 cm ꢃ 0.5 cm) in 0.1 M
TBAP/CH3CN with a cycle time of 100 s.
Table 2 Optical and electrochemical data collected for coloration effi-
ciency measurements of polyamide Ic
Cyclesa
dOD950
Q/mC cmꢁ2
h/cm2 Cꢁ1
Decay (%)e
b
c
d
Polymer synthesis
The synthesis of polyamide Ib was used as an example to illus-
trate the general synthetic route used to produce a series of
polymers. A mixture of 0.24 g (0.5 mmol) of diamine, 4,40-dia-
mino-400-N-phenothiazinyltriphenylamine (4), 0.08 g (0.5 mmol)
of terephthalic acid (5b), 0.07 g of calcium chloride, 0.5 mL of
triphenyl phosphite (TPP), 0.25 mL of pyridine, and 0.5 mL of
N-methyl-2-pyrrolidinone (NMP) was heated with stirring at 105
ꢀC for 3 h. The obtained polymer solution was poured slowly
into 300 mL of stirred methanol giving rise to a stringy, fiberlike
precipitate that was collected by filtration, washed thoroughly
with hot water and methanol, and dried under vacuum at 100 ꢀC.
Reprecipitations of the polymer by DMAc/methanol were
carried out twice for further purification. The inherent viscosity
and weight-average molecular weights (Mw) of the obtained
poly(amine-amide) Ib was 0.29 dL/g (measured at a concentra-
1
0.436
0.434
0.431
0.423
0.418
0.416
0.414
0.411
0.409
0.401
0.399
1.718
1.712
1.704
1.700
1.698
1.693
1.688
1.683
1.676
1.675
1.669
254
254
253
249
246
246
245
244
244
239
239
0
0
10
20
30
40
50
60
70
80
90
100
0.4
2.0
3.1
3.1
3.5
3.9
3.9
5.9
5.9
a
Switching between 0 and 0.95 (V vs. Ag/AgCl). b Optical density change
at 950 nm. Ejected charge, determined from the in situ experiments.
c
d
Coloration efficiency is derived from the equation: h ¼ dOD950/Q.
e
Decay of coloration efficiency after cyclic scans.
ꢀ
1
Fig. 5. The electrochromic CE (h ¼ dOD/Q) and injected charge
(electroactivity) after various switching steps are summarized in
Table 2. The electrochromic behavior of Ic film exhibited high
CE up to 254 cm2 Cꢁ1 (at 970 nm) and 390 cm2 Cꢁ1 (at 865 nm) at
the first and second oxidation stages, respectively, and retained
95% of their electroactivity after hundreds of switching cycles.
tion of 0.5 g/dL in DMAc at 30 C) and 38500, respectively. H
NMR (DMSO-d6, d, ppm): 6.30 (d, 2H, Hc), 6.83 (t, 2H, He), 6.96
(t, 2H, Hd), 7.03 (d, 2H, Hf), 7.13 (d, 2H, Ha), 7.21–7.27 (m, 6H,
Hb + Hh), 7.83 (d, 4H, Hg), 8.10 (s, 4H, Hi), 10.46 (amide-NH).
13C NMR (DMSO-d6, d, ppm): 116.1 (C6), 119.2 (C10), 122.2 (C12
+ C2), 122.8 (C8), 125.8 (C13), 126.8 (C9), 127.5 (C7), 127.9 (C16),
131.6 (C3), 132.8 (C4), 135.5 (C14), 137.7 (C15), 142.7 (C5), 144.2
Conclusion
A series of NIR electroactive polyamides have been readily
prepared from the newly synthesized diamine monomer, 4,40-
diamino-400-N-phenothiazinyltriphenylamine,
and
various
dicarboxylic acids via the phosphorylation polyamidation reac-
tion. Introduction of the electron-donating PSN group to the
polymer main chain not only affords high Tg and good thermal
stability but also leads to good solubility of the polyamides. All
the obtained polymers reveal valuable electrochromic charac-
teristics such as enhanced contrast in the NIR region, unique
purple electrochromic behavior, low switching times, good
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(C11), 147.6 (C1), 164.9 (amide carbonyl). The other polyamides
were prepared by an analogous procedure.
cuvette using a Hewlett-Packard 8453 UV-Visible diode array
spectrophotometer. The ITO-coated glass slide was used as the
working electrode, a platinum wire as the counter electrode, and
a Ag/AgCl cell as the reference electrode. CE (h) determines the
amount of optical density change (dOD) at a specific absorption
wavelength induced as a function of the injected/ejected charge
(Q; also termed as electroactivity) which is determined from the
in situ experiments. CE is given by the equation: h ¼ dOD/Q ¼
log[Tb/Tc]/Q, where h (cm2 Cꢁ1) is the coloration efficiency at
a given wavelength, and Tb and Tc are the bleached and colored
transmittance values, respectively. The thickness of the poly-
amide thin films was measured by an alpha-step profilometer
(Kosaka Lab., Surfcorder ET3000, Japan). Colorimetry
measurements were obtained using a Minolta CS-100A Chroma
Meter. The color coordinates are expressed in the CIE 1931 Yxy
color spaces.
Preparation of the polyamide films
A solution of polymer was made by dissolving about 0.3 g of the
polyamide samples in 8 mL of DMAc or NMP. The homoge-
neous solution was poured into a 9-cm glass Petri dish, which was
placed in a 80 ꢀC oven for 6 h to remove most of the solvent; then
ꢀ
the semidried film was further dried in vacuo at 180 C for 8 h.
The obtained films were about 30–50 mm in thickness and were
used for molecular weight measurements, solubility tests, and
thermal analyses.
Measurements
Fourier transform infrared (FT-IR) spectra were recorded on
a Perkin Elmer RXI FT-IR spectrometer. Elemental analyses
were run in a VarioEL-III Elementar. Fast atom bombardment
(FAB) mass spectra were measured on JEOL MStation JMS-700
mass spectrometer. 1H and 13C nuclear magnetic resonance
(NMR) spectra were measured on a Bruker AV-300 FT-NMR
system and referenced to the DMSO-d6 signal, and peak multi-
plicity was reported as follows: s, singlet; d, doublet; t, triplet; m,
multiplet. The inherent viscosities were determined at 0.5 g/dL
concentration using a Tamson TV-2000 viscometer at 30 ꢀC. Gel
permeation chromatographic (GPC) analysis was performed on
a Lab Alliance RI2000 instrument (one column, MIXED-D from
Polymer Laboratories) connected with a refractive index detector
from Schambeck SFD Gmbh. All GPC analyses were performed
using a polymer/DMF solution at a flow rate of 1 mL minꢁ1 at
Acknowledgements
The authors are grateful to the National Science Council of the
Republic of China for financial support of this work. The tech-
nical assistance on the gel permeation chromatographic
measurement from Prof. Wen-Chang Chen and Dr Chia-Hung
Lin of National Taiwan University is highly appreciated.
References and notes
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ꢀ
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ꢀ
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M
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