Fluorescent and electrochromic aromatic polyamides with 4-tert-butyltriphenylamine chromophore

Article abstract of DOI:10.1002/pola.24033

A new triphenylamine-based aromatic dicarboxylic acid monomer, 4-ferf-butyl-4',4"-dicarboxytriphenylamine (2), was synthesized from the cesium fluoride mediated N,N-diarylation reaction of 4-fert-butylaniline with 4-fluorobenzonitrile and subsequent alkal

Full text of DOI:10.1002/pola.24033

Fluorescent and Electrochromic Aromatic Polyamides with
4-tert-Butyltriphenylamine Chromophore
SHENG-HUEI HSIAO,1 GUEY-SHENG LIOU,2 YI-CHUN KUNG,3 YU-MING CHANG3
1Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, Taipei 10608, Taiwan
2Institute of Polymer Science and Engineering, National Taiwan University, Taipei 10617, Taiwan
3Department of Chemical Engineering, Tatung University, Taipei 10451, Taiwan
Received 5 February 2010; accepted 14 March 2010
DOI: 10.1002/pola.24033
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: A new triphenylamine-based aromatic dicarboxylic
acid monomer, 4-tert-butyl-40,400-dicarboxytriphenylamine (2),
was synthesized from the cesium fluoride mediated N,N-diary-
lation reaction of 4-tert-butylaniline with 4-fluorobenzonitrile
and subsequent alkaline hydrolysis of the dinitrile intermedi-
ate. A series of six aromatic polyamides 4a-4f with tert-butyltri-
phenylamine groups was prepared from the newly synthesized
dicarboxylic acid and various aromatic diamines. These polya-
mides were readily soluble in many organic solvents and could
be solution-cast into flexible and strong films. The glass-transi-
tion temperatures of these polymers were in the range of 274–
311 ꢀC. These polymers exhibited strong UV-vis absorption
bands at 356–366 nm in NMP solution. Their photolumines-
cence spectra showed maximum bands around 433–466 nm in
the blue region. Cyclic voltammograms of all the polyamides
exhibited reversible oxidation redox couples in acetonitrile.
The polyamide 4f, with tert-butyltriphenylamine segment in
both diacid and diamine residues, exhibited stable electrochro-
mic characteristics with a color change from a colorless neutral
form, through a green semioxidized form, to a deep purple
C
V
fully oxidized form. 2010 Wiley Periodicals, Inc. J Polym Sci
Part A: Polym Chem 48: 2798–2809, 2010
KEYWORDS: cyclic voltammetry; electrochemistry; electro-
chromism; fluorescence; polyamides; spectroelectrochemistry;
triphenylamine
INTRODUCTION Triarylamines are an important class of aro-
matics because they are easily oxidized to form stable ami-
nium cation radicals. In view of their stability, triarylamine
cation radicals have become promising spin-containing units
for exploitation of potential organic magnetic materials.1–5
Perhaps most commonly, triarylamine derivatives have been
used as the hole-transport and/or light-emitting materials in
electroluminscent devices.6–10 Most of triarylamine deriva-
tives are used as vapor-deposited thin films, or composite
materials dispersed in an inert polymer binder. It is, how-
ever, difficult to maintain long-term morphological stability
due to crystallization or phase separation. One of the meth-
ods to overcome this drawback could be the incorporation of
triarylamine units into the polymer backbone or into its side
chains.11–15 The extensive investigations on the polymeric
materials have shown the possibility of enhancing the
device performance due to the increased morphological sta-
bility.16–20 In addition, the uses of polymeric materials
exhibit another advantages, such as good processability and
variety of possible chemical modification.21–26
and strong hydrogen bonding results in high melting or
glass-transition temperatures (Tgs) and limited solubility in
most organic solvents.27,28 These properties make them gen-
erally intractable or difficult to process, thus restricting their
applications. To overcome such a difficulty, polymer structure
modification becomes necessary. It has been reported that
aromatic polyamides bearing the propeller-shaped triphenyl-
amine (TPA) unit in the main chain were amorphous
and easily soluble in organic solvents and they could be
solution-cast into flexible films with good mechanical prop-
erty and high thermal stability.29–31 In recent years, we
have demonstrated that TPA-based polymers are promising
hole-transporting and electrochromic materials for optoelec-
tronic applications due to the electroactive TPA units.32–42 It
has also been reported in our previous publications36,41,42
that the incorporation of electron-donating substituents
such as tert-butyl and methoxy groups on the electro-
chemically active sites of the TPA unit resulted in stable
TPA cationic radicals and decreased oxidation potential, lead-
ing to a significantly enhanced redox and electrochromic
stability of the prepared polyamides. In an effort to extend
our work to the design and synthesis of electrochromic high-
performance polymers, herein we wish to synthesize a new
Wholly aromatic polyamides are characterized as highly ther-
mally stable polymers with a favorable balance of physical
and chemical properties. However, rigidity of the backbone
Additional Supporting Information may be found in the online version of this article. Correspondence to: S.-H. Hsiao (E-mail: shhsiao@ntut.edu.tw)
C
V
Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 2798–2809 (2010) 2010 Wiley Periodicals, Inc.
2798
INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE
tert-butyl-substituted TPA-based dicarboxylic acid, namely 4-
tert-butyl-40,400-dicarboxytriphenylamine, and its derived aro-
matic polyamides. The optoelectronic and fluorescence prop-
erties of the prepared polymers were also investigated. As
compared to the corresponding counterparts derived from
4,40-diamino-400-tert-butyltriphenylamine and aromatic dicar-
boxylic acids we reported previously,34 the present poly-
amides exhibited a slightly higher oxidation potential, but
with a stronger fluorescence intensity and different colora-
tion changes upon electrochemical oxidation.
(125 MHz, CDCl3, d, ppm): 150.7 (C7), 150.2 (C6), 142.6 (C3),
133.9 (C9), 127.6 (C4), 127.0 (C5), 123.1 (C8), 119.4
(-CN), 105.9 (C10), 35.1 (C2), 31.8 (C1). Crystal data for 1:
yellow single crystal grew by the slow crystallization from
ethanol, crystal dimensions: 0.5 ꢂ 0.4 ꢂ 0.3 mm3, Mono-
clinic, space group
P
21/a,
a
¼
12.3393(4) Å,
b
¼
13.3826(4) Å, c ¼ 12.4031(5) Å, a ¼ 90ꢀ, b ¼ 97.8470ꢀ
(10), c ¼ 90ꢀ, Dcalcd ¼ 1.150 mg/m3, Z ¼ 4, and V ¼
2028.97(12) Å3.
EXPERIMENTAL
Materials
4-tert-Butylaniline (Acros), 4-fluorobenzonitrile (TCI), sodium
hydride (NaH; Fluka), and triphenyl phosphite (TPP, Acros)
were used without further purification. N,N-Dimethylaceta-
mide (DMAc, Fluka), N,N-dimethylformamide (DMF, Acros),
pyridine (Py, Wako), and N-methyl-2-pyrrolidone (NMP, Fluka)
were dried over calcium hydride for 24 h, distilled under
reduced pressure, and stored over 4 Å molecular sieves in a
sealed bottle. According to the previously reported proce-
dures,43 the CF3-containing diamine, 2-trifluoromethyl-4,40-
diaminodiphenyl ether (3d) (mp ¼ 112–113 ꢀC), was pre-
pared from the chloro-displacement reaction of 2-chloro-5-
nitrobenzotrifluoride with 4-nitrophenol in the presence of
potassium carbonate, followed by Pd/C-catalyzed hydrazine
reduction. 4,40-Diamino-400-tert-butyltriphenylamine (3f) (mp
¼ 113–115 ꢀC) was prepared by the cesium fluoride-mediated
aromatic nucleophilic substitution reaction of 4-fluoronitro-
benzene with the 4-tert-butylaniline followed by Pd/C-cata-
lyzed hydrazine reduction, as described in one of our previous
publications.34 Commercially available aromatic diamines
such as p-phenylenediamine (3a, TCI), m-phenylenediamine
(3b, Acros), 4,40-diaminophenyl ether (3c, TCI), and 9,9-bis(4-
aminophenyl)fluorene (3e, TCI) were used as received. Com-
mercially obtained calcium chloride was dried under vacuum
at 150 ꢀC for 6 h before use. Tetrabutylammonium perchlorate
(TBAP, TCI) was recrystallized twice from ethyl acetate and
then dried in vacuum before use.
4-Tert-butyl-40,400-dicarboxytriphenylamine (2)
A mixture of 9.56 g of potassium hydroxide and 5.0 g of the
obtained dinitrile compound 1 in 50 mL of ethanol and 50
mL of distillated water was refluxed at 100 ꢀC until no fur-
ther ammonia was generated. The time taken to reach this
stage was about 3 days. The solution was cooled, and the pH
value was adjusted by conc. hydrochloric acid (12 M) to
near 3. The white precipitate formed was collected by filtra-
tion, washed thoroughly with water, and dried in vacuo to
give 4.6 g (yield ¼ 83%) of diacid 2 (mp ¼ 292–294 ꢀC by
DSC at 2 ꢀC/min). IR (KBr): 1686 cmꢁ1 (C¼¼O stretch),
2700–3400 cmꢁ1 (OAH).
1H NMR (500 MHz, DMSO-d6, d, ppm): 7.85 (d, J ¼ 8.6 Hz,
4H, Hd), 7.42 (d, J ¼ 8.5 Hz, 2H, Ha), 7.07 (d, J ¼ 8.5 Hz, 2H,
Hb), 7.04 (d, J ¼ 8.6 Hz, 4H, Hc), 1.28 (s, 9H, tert-butyl). 13C
NMR (125 MHz, DMSO-d6, d, ppm): 166.8 (C¼¼O), 150.3 (C7),
147.9 (C6), 142.9 (C3), 130.9 (C9), 129.1 (C4), 126.8 (C5),
126.0 (C10), 122.9 (C8), 34.2 (C2), 31.0 (C1).
Monomer Synthesis
4-Tert-butyl-40,400-dicyanotriphenylamine (1)
A mixture of 4.0 g (0.1 mol) of 60% sodium hydride in 80
mL of dry DMSO was stirred at room temperature. To the
mixture, 7.46 g (0.05 mol) of 4-tert-butylaniline and 12.1 g
(0.1 mol) of 4-fluorobenzonitrile were slowly added in
sequence. The mixture was heated with stirring at 120 ꢀC
for 12 h. After cooling, the mixture was poured into 300 mL
of aqueous sodium chloride solution, and the sticky product
gradually solidified after being soaked in ethanol. Recrystalli-
zation from ethanol yielded 9.3 g (53% yield) of pure dini-
trile compound 1 as yellow crystals [mp ¼ 188–189 ꢀC,
measured by differential scanning caloriꢁm1etry (DSC) at a
ꢀ
scan rate of 2 C/min]. IR (KBr): 2217 cm (-C:N stretch).
Synthesis of Polyamides
1H NMR (500 MHz, CDCl3, d, ppm): 7.51 (d, J ¼ 8.6 Hz, 4H,
Hd), 7.40 (d, J ¼ 8.5 Hz, 2H, Ha), 7.11 (d, J ¼ 8.6 Hz, 4H, Hc),
7.05 (d, J ¼ 8.5 Hz, 2H, Hb), 1.28 (s, 9H, tert-butyl). 13C NMR
The synthesis of polyamide 4a is used as an example to
illustrate the general synthetic route used to produce the
polyamides. A 50 mL round-bottom flask equipped with a
FLUORESCENT & ELECTROCHROMIC POLYAMIDES, HSIAO ET AL.
2799

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
temperature with film specimens (0.5 cm width, 6 cm
length), and an average of at least three individual determi-
nations was reported. Thermogravimentric analysis (TGA)
was conducted with a Perkin–Elmer Pyris 1 TGA. Experi-
ments were carried out on approximately 3–5 mg of samples
heated in flowing nitrogen or air (gas flow rate ¼ 40 cm3/
ꢀ
min) at a heating rate of 20 C/min. DSC analyses were per-
formed on a Perkin–Elmer Pyris 1 DSC at a scan rate of 20
ꢀC/min in flowing nitrogen. Thermomechanical analysis
(TMA) was conducted with a Perkin–Elmer TMA 7 instru-
ment. The TMA experimꢀents were conducted from 50 to 350
ꢀC at a scan rate of 10 C/min with a penetration probe 1.0
mm in diameter under an applied constant load of 10 mN.
Softening temperatures (Ts) were taken as the onset temper-
atures of probe displacement on the TMA traces. Ultraviolet-
visible (UV-Vis) spectra of the polymer films were recorded
on an Agilent 8453 UV-Visible spectrophotometer. Electro-
chemistry was performed with a CH Instruments 611C elec-
trochemical analyzer. Voltammograms are presented with the
positive potential pointing to the left and with increasing an-
odic currents pointing downwards. Cyclic voltammetry was
conducted with the use of a three-electrode cell in which
ITO (polymer films area ca. 0.8 cm ꢂ1.25 cm) was used as a
working electrode. A platinum wire was used as an auxiliary
electrode. All cell potentials were taken with the use of a
homemade Ag/AgCl, KCl (sat.) reference electrode. Ferrocene
was used as an external reference calibration (þ0.44 V vs.
Ag/AgCl). Spectroelectrochemistry analyses were carried out
with an electrolytic cell whcih was composed of a 1 cm cuv-
ette, ITO as a working electrode, a platinum wire as an
SCHEME 1 Synthetic route to the target dicarboxylic acid
monomer 2.
magnetic stirrer was charged with 0.3895 g (1.00 mmol) of
diacid 2, 0.1081 g (1.00 mmol) of p-phenylenediamine (3a),
1 mL of TPP, 2 mL of NMP, 0.5 mL of pyridine, and 0.2 g of
calcium chloride (CaCl2). The reaction mixture was heated
with stirring at 120 ꢀC for 3 h. The polymer solution was
poured slowly into 200 mL of stirring methanol giving rise
to a stringy, fiber-like precipitate that was collected by filtra-
tion, washed thoroughly with hot water and methanol, and
dried. The other polyamides were prepared by an analogous
procedure. IR (film): 3315 cmꢁ1 (amide NAH stretch), 1649
cmꢁ1 (amide C¼¼O stretch), 2962 cmꢁ1 (tert-butyl C-H
stretch).
auxiliary electrode, and
a Ag/AgCl reference electrode.
Absorption spectra in the spectroelectrochemical experi-
ments were measured with an Agilent 8453 UV-Visible diode
array spectrophotometer. Photoluminescence (PL) spectra
were measured with a Varian Cary Eclipse fluorescence
spectrophotometer.
Preparation of the Polyamide Films
A polymer solution was made by the dissolution of about
0.5 g of the polyamide sample in 10 mL of hot DMAc. The
homogeneous solution was poured into a 9-cm glass Petri
dish, which was placed in a 90 ꢀC oven overnight for the
slow release of the solvent, and then the film was stripped
off from the glass substrate and further dried in vacuum at
RESULTS AND DISCUSSION
ꢀ
Monomer Synthesis
160 C for 6 h. The obtained films were about 0.08 lm thick
As depicted in Scheme 1, the new aromatic dicarboxylic acid
2 was successfully synthesized by the alkaline hydrolysis
reaction of the dinitrile compound 1, which was obtained
from the condensation reaction of 4-tert-butylaniline with 4-
fluorobenzonitrile in DMSO in the presence of sodium
hydride. IR, 1H NMR and 13C NMR spectroscopic techniques
were used to identify the structures of the intermediate dini-
trile compound 1 and the targeted dicarboxylic acid mono-
mer 2. The IR spectrum (see Supporting Information Fig. S1)
of dinitrile compound 1 gave a characteristic absorption
peak at 2217 cmꢁ1 (C:N stretching). After hydrolysis, the
characteristic absorption of the cyano group disappeared,
and the carboxylic acid group showed a typical carbonyl
absorption band at 1686 cmꢁ1 (C¼¼O stretching) together
with the appearance of broad bands around 2700–3400
cmꢁ1 (OAH stretching). The structures of 1 and 2 were also
confirmed by high-resolution NMR spectra. The 1H and 13C
NMR spectra of these compounds are illustrated in Figures 1
and were used for X-ray diffraction measurements, tensile
tests, solubility tests, and thermal analyses.
Measurements
Infrared spectra were recorded on a Horiba FT-720 FTIR
spectrometer. Elemental analyses were run in a Perkin–
Elmer 2400 CHN analyzer. 1H and 13C NMR spectra were
measured on a Bruker AVANCE 500 FT-NMR system. The in-
herent viscosities were determined with a Cannon-Fenske
viscometer at 30 ꢀC. Wide-angle X-ray diffraction (WAXD)
measurements were performed at room temperature (ꢃ25
ꢀC) on a Shimadzu XRD-6000 X-ray diffractometer (40 kV, 30
mA), using nickel-filtered Cu-Ka radiation (k ¼ 1.5418 Å).
ꢀ
The scanning rate was 2 /min over a range of 2h ¼ 10–40ꢀ.
A universal tester LLOYD LRX with a load cell 5 kg was used
to study the stress-strain behavior of the samples. A gauge
length of 2 cm and a crosshead speed of 5 mm/min were
used for this study. Measurements were performed at room
2800
INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE
the polymerizations proceeded homogeneously throughout
the reaction and afforded clear, highly viscous polymer
solutions. These polymers precipitated in a tough, fiber-
like form when the resulting polymer solutions were
slowly poured into methanol with stirring. These poly-
amides were obtained in almost quantitative yields, with
inherent viscosity in the range of 0.55–0.90 dL/g
(Table 1). All the polymers could be solution-cast into
flexible and tough films, and this was indicative of the
formation of high molecular weight polymers. The IR
spectrum of the polyamide 4a shown in Supporting Infor-
mation Figure S2 exhibited the characteristic amide
absorptions near 3300 and 1650 cmꢁ1, sustaining the
formation of the amide linkages. The 1H and 13C NMR of
the representative polyamide 4a agree well with the
desired structure (Fig. 4).
FIGURE 1 1H NMR spectra of (a) dinitrile compound 1 and (b)
dicarboxylic acid monomer 2 in DMSO-d6.
and 2, respectively. The assignments of each carbon and pro-
ton also are given in the figures, and these spectra are in
good agreement with the proposed molecular structures. The
13C NMR spectra confirm that the cyano groups were
completely converted into the carboxyl groups by the disap-
pearance of the resonance peak for the cyano carbon at
119.4 ppm and the appearance of the carbonyl peak at
166.8 ppm. The signals appeared at 1.28 ppm in the 1H
NMR spectrum and 34.2 ppm (a quaternary carbon) and
31.0 ppm (a methyl carbon) in the 13C NMR spectrum are
assigned to the tert-butyl groups. The molecular structure of
1 was further determined by single-crystal crystallographic
analysis (Fig. 3), and the bond length and angle data are
summarized in Supporting Information Table S1. As shown
in Figure 3, compound 1 displays a propeller-like geometry
of the TPA core. This three-dimensional structure together
with the bulky tert-butyl group will hinder the close packing
of polymer chain and enhance the solubility of formed
polyamides.
Polymer Synthesis
A series of new aromatic polyamides, 4a–4f, were pre-
pared from diacid 2 and six aromatic diamines (3a–3f)
by the Yamazaki-Higashi polyamidation reaction44 using
TPP and pyridine as condensing agents (Scheme 2). All
FIGURE 2 (a) 13C NMR spectrum of compound 1 in CDCl3. (b)
13C NMR spectrum of 4-tert-butyl-40,400-dicarboxytriphenylamine
(2) in DMSO-d6.
FLUORESCENT & ELECTROCHROMIC POLYAMIDES, HSIAO ET AL.
2801

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
and dimethyl sulfoxide (DMSO) at room temperature or
upon heating at 80 ꢀC. They were also soluble in phenol-
type solvents such as m-cresol; however, they were insoluble
in less polar solvents like THF. From the diffraction patterns
shown in Supporting Information Figure S3, the X-ray diffrac-
tion studies of the polyamides indicated that all the poly-
mers are essentially amorphous. The excellent solubility and
amorphous nature of these polyamides can be attributed to
the increased free volume caused by the introduction of the
three-dimensional TPA moiety and bulky pendent tert-butyl
substituents into the backbone. Thus, the excellent solubility
makes these polymers as potential candidates for practical
applications by low-cost spin-coating or inkjet-printing pro-
cesses. The mechanical properties of the polymer films are
summarized in Supporting Information Table S2. They had
a tensile strength of 85–97 MPa, an elongation at break of
7–10%, and a tensile modulus of 2.1–2.6 GPa, indicating
strong and tough polymeric materials.
Thermal Properties
The thermal properties of the polyamides were investigated
by TGA, DSC and TMA. The results are summarized in Table
2. The glass-transition temperatures (Tg) of all the 4 series
polymers were observed in the range 274–311 ꢀC by DSC.
Polyamide 4e showed the highest Tg due to the presence of
rigid 9,9-diphenylfluorene unit. The softening temperatures
(Ts) 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 displace-
ment on the TMA trace. A typical TMA trace of polyamide 4a
is illustrated in Figure 5. In almost all cases, the Ts values
obtained by TMA are comparable to the Tg values measured
FIGURE 3 Molecular structure of dicyano compound 1 by single
crystal X-ray analysis. [Color figure can be viewed in the online
issue, which is available at www.interscience.wiley.com.]
Polymer Properties
Organo-Solubility and Film Property
The solubility properties of the polyamides in several organic
solvents at 10% (w/v) are also reported in Table 1. All the
polymers exhibited good solubility in a variety of dipolar sol-
vents such as NMP, DMAc, N,N-dimethylformamide (DMF),
SCHEME 2 Synthesis of polyamides.
2802
INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE
TABLE 1 Inherent Viscosity and Solubility Behavior of Polyamides
Solubility in Various Solventsb
Polymer Code
ginh (dL/g)a
NMP
DMAc
DMF
DMSO
m-Cresol
THF
4a
4b
4c
4d
4e
4f
0.74
0.57
0.90
0.64
0.69
0.55
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
b
þþ: soluble at room temperature; þ: soluble on heating at 80 ꢀC or boil-
Qualitative solubility was determined by using 10 mg sample in 1 mL
of stirred solvent. NMP N-methyl-2-pyrrolidone; DMAc N,N-di-
ing temperature; ꢁ: insoluble even on heating.
¼
¼
a
Inherent viscosity measured at a concentration of 0.5 g/dL in DMAc
methylacetamide; DMF ¼ N,N-dimethylformamide; DMSO ¼ dimethyl
ꢁ5 wt % LiCl at 30 ꢀC.
sulfoxide; THF ¼ tetrahydrofuran.
by the DSC experiments. Typical TGA thermograms for poly-
amide 4a are also included in Figure 5. All of the polymers
exhibited reasonable thermal stability. They started to
decompose around or above 460 ꢀC and lost 10% weight
between 469ꢃ520 ꢀC and 475ꢃ543 ꢀC in nitrogen and air
atmosphere, respectively. These polymers afforded high
anaerobic char yield in the range of 63–67% at 800 ꢀC in a
nitrogen atmosphere. It implied that these polymers still
showed good thermal stability irrespective of introducing
tert-butyl groups in the polymer side chain. For comparison,
the thermal behavior data of analogous polyamide 40 on the
basis of 4,40-dicarboxytriphenylamine are also listed in Table
2. Except for 4b, the 4 series polyamides showed a slightly
decreased Tg as compared to the corresponding 40 series
polyamides. This may be accounted for the increased free vol-
ume caused by the introduction of the bulky tert-butyl group
in the repeat unit. The 4 series polyamides also revealed a
slightly decreased thermal stability than the corresponding 40
analogs. This is reasonable in consideration of the presence of
less stable aliphatic segment (tert-butyl group).
through steric hindrance and inductive effect (by decreasing
the electron-donating character of diamine moieties). The
significantly decreased quantum efficiency (UPL ¼ 1.4%) of
polyamide 4a when compared with polyamide 4b (UPL
¼
12.9%) seems to indicate possible charge-transfer quenching
effect exerting in the former due to the p-phenylenediamine
residue. In comparison to the corresponding counterparts
derived from 4,40-diamino-400-tert-butyltriphenylamine (i.e.,
diamine 3f) and aromatic dicarboxylic acids we reported
earlier,34 the present polyamides exhibited a stronger fluo-
rescence intensity. This may be rationalized by the fact that
the TPA structure is inserted between the carboxyl function-
alities for the present polyamides. This possibly decreases
the nonradiative charge-transfer interactions between the
diamine residue (donor) and the benzoyl unit (acceptor).
The very low UPL value (0.2%) associated with polyamide 4f
possibly could be attributed to the fact that its excited-state
energy is more likely released by vibrational relaxation
because of the greater conformational mobility. The polymer
Absorption and Fluorescence Properties
The optical properties of these polymers were investigated
by UV-vis absorption and photoluminescence (PL) spectros-
copy. The results are summarized in Table 3. Figure 6 shows
the UV-vis absorption and PL emission profiles of four
selected polyamides. All the polyamides exhibited strong UV-
vis absorption bands at 356–366 nm in NMP solution, as-
signable to the p–p* transitions. Their PL spectra in NMP so-
lution showed maximum bands around 432–498 nm corre-
sponding to blue color (see Fig. 7), with quantum yields
(UPL) of 0.2–16.5% relative to the quinine sulfate standard
(assuming UPL ¼ 54.6%).45 The highest fluorescence quan-
tum yield of 16.5% was observed for polyamide 4e due to
the bulky, rigid 9,9-diphenylfluorene moiety. A relatively
higher quantum yield of polyamide 4d (UPL ¼ 15.6%) in
comparison to structurally similar 4c (UPL ¼ 5.1%) can be
rationalized by the fact that the bulky trifluoromethyl
(ACF3) group decreased the rotational freedom of the ether
linkage and its presence might effectively reduce charge
transfer formation within or between polymer chains
FIGURE 4 (a) 1H NMR and (b) 13C NMR spectra of polyamide
4a in DMSO-d6. [Color figure can be viewed in the online issue,
which is available at www.interscience.wiley.com.]
FLUORESCENT & ELECTROCHROMIC POLYAMIDES, HSIAO ET AL.
2803

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 2 Thermal Properties of Polyamidesa
Td (ꢀC)d
Polymer Code
Tg (ꢀC)b
Ts (ꢀC)c
In N2
In Air
Char Yield (wt %)e
4a
4b
4c
4d
4e
4f
288
286
274
281
311
303
293
271
280
316
287
284
269
274
316
298
288
270
277
318
484
484
469
478
520
510
496
505
495
538
478
502
489
475
543
511
513
512
496
540
67
67
65
63
63
64
70
74
67
66
40a
40b
40c
40e
a
The polymer film sample were heated at 300 ꢀC for 1 h before all the
thermal analyses.
b
Midpoint temperature of baseline shift on the heating DSC trace (from
50 to 400 ꢀC at 20 ꢀC/min).
c
Softening temperature taken as the onset temperature of the
probe displacement on the TMA trace at
a heating rate of 10
ꢀC/min.
d
Decomposition temperature at which
a
10 wt loss was
%
recorded by TGA at
rate of 40 cm3/min.
a
heating rate of 20 ꢀC/min and
a gas flow
e
Residual weight percentages at 800 ꢀC in nitrogen.
films were also measured for optical transparency using UV-
vis spectroscopy, and the cutoff wavelengths (absorption
edge; konset) were recorded in the range of 406–432 nm
(Supporting Information Fig. S4).
cal species. Nevertheless, CV measurements show that poly-
mers 4a-4e undergo a reversible process, reflecting high oxi-
dation stability, due to the substitution of tert-butyl group.
For the 40 series polyamides (see Table 3), they generally
possessed an irreversible redox behavior in the anodic oxida-
tive scanning. Thus, the good elelctrochemical redox revers-
ibility for the 4 series polymers confirms that para-substitu-
tion of the tert-butyl group on the TPA unit results in an
enhanced stability to the radical cation species. In general,
the present series polyamides revealed a similar redox sta-
bility to that of the methoxy-substituted analogs reported
previously.35
Electrochemical Properties
The redox behavior of these polyamides was investigated by
cyclic voltammetry (CV) for the cast films on an ITO-coated
glass substrate as working electrode in 0.1 M TBAP/acetoni-
trile (CH3CN) solution. The redox potentials of the poly-
amides as well as their highest occupied molecular orbital
(HOMO) and lowest unoccupied molecular orbital (LUMO)
energy levels (below vacuum) are also listed in Table 3.
Figure 8(b) depicts the CV curve of polyamide 4e, which was
representative for the other polyamides 4a to 4d. Polyamide
4e exhibited a single and well-defined reversible redox cou-
ple, with oxidation half-wave potential (E1/2) at 1.14 V ver-
sus Ag/AgCl, when the potential was scanned between 0.0
and 1.4 V. We noted that the color of polyamide 4e film
changed from colorless to pale blue upon oxidation. Polya-
mides 4a-4d showed very similar CV curves to that of 4e,
with E1/2 values ranging from 1.15 to 1.18 V. It is notewor-
thy to mention that changing the diamine structure did
not significantly affect the oxidation of the TPA cores of
polymers 4a-4e. It is also can be seen that the oxidation of
polyamides 4a-4e is less facile than that of analogues based
on 4,40-diamino-400-tert-butyltriphenylamine (E1/2 ¼ 0.80–
0.85 V)34 owing to the electron-withdrawing effect of the
remaining carbonyl groups that destabilize the cationic radi-
As can be seen from Figure 8(c), polyamide 4f exhibits two
redox amino centers in each repeat unit and shows two cor-
responding well-defined, quasi-reversible anodic redox cou-
ples. The first oxidation at E1/2 ¼ 0.85 V appears to involve
one electron loss from the TPA unit in the diamine residue,
and the second oxidation wave (E1/2 ¼ 1.27 V) is related to
the electron loss from the TPA unit in the diacid residue. In
fact, the first oxidation potential is found to be similar to
those of polyamides derived from diamine 3f and conven-
tional aromatic dicarboxylic acids.34
A clear coloration
change was also observed for the film of 4f upon oxidation,
from colorless to green and then to purple.
The external ferrocene/ferrocenium (Fc/Fcþ) rodox standard
has E1/2 at 0.44 V versus Ag/AgCl in acetonitrile. Under the
assumption that the HOMO level for the ferrocene standard
was 4.80 eV with respective to the zero vacuum level, the
2804
INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE
FIGURE 5 TMA and TGA curves of polyamide 4a with a heating
10 and 20 ꢀC/min, respectively. [Color figure can be viewed in the
online issue, which is available at www.interscience.wiley.com.]
FIGURE 6 UV-vis absorption and PL spectra of polyamides 4b,
4c, 4d, and 4e with a concentration of 1 ꢂ 10ꢁ5 M in NMP. Qui-
nine sulfate dissolved in 1N H2SO4(aq) (1 ꢂ 10ꢁ5 M) as the stand-
ard (UF ¼ 54.6%). Data indicated in parentheses are the emission
maximum of the PL spectra. [Color figure can be viewed in the
online issue, which is available at www.interscience.wiley.com.]
HOMO levels for the 4 series polyamides were estimated to
be 4.99–5.40 eV calculated from the onset oxidation poten-
tials (Eonset). These data together with absorption spectra
were then used to obtain the LUMO energy levels. These
polyamides have good hole-injection and hole-transporting
ability, because their HOMOs are close to the common hole-
injection materials such as PEDOT:PSS (ꢃ5.2 eV).46
preparations and solution conditions were identical to those
used in CV. The polymers were drop-coated as films on ITO/
glass substrates and mounted in a spectroelectrochemical
cell. The typical absorption spectral changes of polyamide 4e
(representative for the 4a–4e series) are shown in Figure 9.
The oxidation of 4e started to occur at 1.10 V. When the
applied potential was gradually increased from 1.10 to
1.35 V, the absorbption band at 360 nm decreased and a
Spectroelectrochemical and Electrochromic Properties
Following the electrochemical tests, the optical properties of
the electrochromic films were evaluated by using spectroe-
lectrochemistry at different applied potentials. The electrode
TABLE 3 Optical and Electrochemical Properties of Polyamides
Oxidation Potential
(V)e
E1/2
Code
Abs kmax (nm)a
Abs konset (nm)b
PL kmax (nm)c
UPL (%)d
1st
2nd
Eonset
Eogpt (eV)f
EHOMO/LUMO (eV)g
4a
4b
4c
4d
4e
4f
364 (370)
358 (364)
356 (358)
358 (365)
356 (363)
366 (368)
365 (361)
356 (361)
355 (361)
355 (360)
413
410
406
411
416
432
408
405
414
412
458
432
442
439
433
498
421
421
419
423
1.4
12.9
5.1
1.18
–
1.00
1.01
1.03
1.03
1.04
0.63
1.02
1.02
1.03
1.02
3.00
3.02
3.05
3.02
2.98
2.87
3.03
3.06
3.00
3.01
5.36/2.36
5.37/2.35
5.39/2.34
5.39/2.37
5.40/2.42
4.99/2.12
5.38/2.35
5.38/2.32
5.39/2.39
5.38/2.37
1.15
–
1.17
–
15.6
16.5
0.2
1.16
–
1.14
–
0.85
1.27
40a
40b
40c
40e
a
1.2
(1.18)h
(1.16)h
(1.19)h
1.15
–
–
–
–
9.6
3.8
11.5
e
UV/vis absorption measured in NMP (10ꢁ5 M) at room temperature.
Determined by cyclic voltammetry versus Ag/AgCl in acetonitrile.
The data were calculated of thin film by the equation: Eogpt (optical
f
Data shown in parentheses are those measured as thin solid-film.
b
Absorption edge (konset
)
measured in thin solid-film at room
band gap) ¼ 1240/konset of polymer films.
g
temperature.
The HOMO energy levels were calculated from Eonset and were refer-
c
PL spectra measured in NMP (10ꢁ5 M) at room temperature.
enced to ferrocene (4.8 eV). ELUMO ¼ EHOMO ꢁ Egopt
.
d
h
The quantum yield was measured by using quinine sulfate (dissolved
Irreversible oxidative process.
in 1 N H2SO4 with a concentration of 1 ꢂ 10ꢁ5 M, assuming photolumi-
nescence quantum efficiency of 54.6%) as
temperature.
a standard at room
FLUORESCENT & ELECTROCHROMIC POLYAMIDES, HSIAO ET AL.
2805

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 7 Photos of the solutions
in NMP and solid films of the
selected polyamides before and
upon exposure to a standard lab-
oratory UV lamp (Excited at 365
nm). Quinine sulfate (QS) dis-
solved in 1N H2SO4 (aq) (1
ꢂ
10ꢁ5 M) is used as a reference
(UF ¼ 54.6%).
new broad absorption band around 703 nm started to inten-
sify due to the cation radical formation. As shown in the
inset of Figure 9, polyamide 4e is almost colorless in the
neutral state and pale blue in the oxidized state. Electrochro-
mic switching studies were performed to monitor the
absorbance changes as a function of time and to determine
the switching time of the polymer at its absorption maxi-
mum by stepping potential repeatedly between the neutral
and oxidized states. The switching time was defined as the
time that was required to reach 90% of the full change in
absorbance after switching potential because it is difficult to
perceive any further color change with naked eye beyond
this point. Thin films from polyamide 4e would require 4.4 s
at 1.35 V for reaching 90% absorbance at 703 nm and 2.7 s
for bleaching. After several successive switchings between
0.0 and 1.35 V, the polymer films still exhibited fast response
time and good redox and electrochromic stability (Fig. 10).
it can be seen that the film of 4f switches from a transmis-
sive neutral state (almost colorless) to a highly absorbing
semioxidized state (green) and
a fully oxidized state
In addition, spectroelectrochemistry of polyamide 4f was
also investigated. As displayed in Figure 11, in the neutral
form, at 0 V, the film exhibited strong absorption at wave-
length around 366 nm due to p–p* transition of the polymer,
but it was almost transparent in the visible region. Upon oxi-
dation of the 4f film (increasing applied voltage from 0 to
1.0 V), the intensity of the absorption peak at 366 nm gradu-
ally decreased while a new broadband having its maximum
absorption wavelength at 805 nm gradually increased in
intensity. We attribute this spectral change to the formation
of a stable monocation radical originating from the oxidation
of the amino center in the diamine residue of polymer 4f.
Further increase the applied electric potential to 1.55 V led
to the drop of the absorption intensity at 805 nm with the
concomitant increase of the intensity at 539 and 709 nm.
This spectral change indicated the occurrence of the second
oxidation arising from another TPA unit in the diacid compo-
nent. The observed absorption changes in the film of 4f at
various potentials are fully reversible and are associated
with strong color changes; indeed, they even can be seen
readily by the naked eye. From the inset shown in Figure 11,
FIGURE 8 Cyclic voltammograms of (a) ferrocene, (b) polyamide
4e, and (c) polyamide 4f film on an ITO-coated glass substrate in
the CH3CN solution containing 0.1 M TBAP with a scan rate ¼
100 mV/s. The arrows indicate the film color change during scan.
2806
INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE
FIGURE 11 Spectral change of polyamide 4f thin film on the
ITO-coated glass substrate (in CH3CN with 0.1 M TBAP as the
supporting electrolyte) along with increasing of applied voltage
(vs. Ag/AgCl couple as reference). The inset shows the photo-
graphic images of the film at indicated applied voltages. [Color
figure can be viewed in the online issue, which is available at
www.interscience.wiley.com.]
FIGURE 9 Spectral change of polyamide 4e thin film on the
ITO-coated glass substrate (in CH3CN with 0.1 M TBAP as the
supporting electrolyte) along with increasing of applied voltage
(vs. Ag/AgCl couple as reference). The inset shows the photo-
graphic images of the film at indicated applied voltages. [Color
figure can be viewed in the online issue, which is available at
www.interscience.wiley.com.]
and the green colored oxidized state. Coloration efficiency
(CE; g) 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 coloration
efficiencies (g ¼ DOD/Q)47,48 of the polymer films of 4f after
various switching cycles are summarized in Table 4. Colora-
tion efficiency of 4f was found to be 110 cm2/C at 100% full
switch at 805 nm. After 100 switching cycles between 0 V
and 1.00 V, the film of polyamide 4f only showed 4.5% decay
on coloration efficiency. Therefore, the results of these
(purple). For optical switching studies, the polymer film of
4f was cast on an ITO-coated glass slide, and the film was
potential stepped between its neutral (0 V) and semioxidized
(þ1.0 V) state. While the potential was switched, the absorb-
ance at 805 nm was monitored as a function of time. As
depicted in Supporting Information Figure S5, thin film of
polyamide 4f required 3.1 s at 1.00 V for coloring and 2.1 s
for bleaching. Switching data for the cast film of polyamide
4f are given in Figure 12. The polyamides switch rapidly
(within 4 s) between the highly transmissive neutral state
FIGURE 10 (a) Potential step absorptometry and (b) current con-
sumption of the polyamide 4e film on the ITO-coated glass sub-
strate (active area ꢃ1 cm2) during the continuous cyclic test by
switching potentials between 0 V and 1.35 V (vs. Ag/AgCl) with a
cycle time of 24 s. [Color figure can be viewed in the online
issue, which is available at www.interscience.wiley.com.]
FIGURE 12 (a) Potential step absorptometry and (b) current con-
sumption of the polyamide 4f film on the ITO-coated glass sub-
strate (active area ꢃ1 cm2) during the continuous cyclic test by
switching potentials between 0 V and 1.0 V (vs. Ag/AgCl) with a
cycle time of 20 s. [Color figure can be viewed in the online
issue, which is available at www.interscience.wiley.com.]
FLUORESCENT & ELECTROCHROMIC POLYAMIDES, HSIAO ET AL.
2807

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
8 Shirota, Y.; Okumoto, K.; Inada, H. Synth Met 2000, 111–112,
TABLE 4 Optical and Electrochemical Data Collected for the
Coloration Efficiency Measurements of Polyamide 4f
387–391.
9 Thelakkat, M. Macromol Mater Eng 2002, 287, 442–461.
10 Shirota, Y.; Kageyama, H. Chem Rev 2007, 107, 953–1010.
Switching
Cyclesa
Q
g
DODb
(mC/cm2)c
(cm2/C)d
Decay (%)e
11 Liang, F.; Pu, Y.-J.; Kurata, T.; Kido, J. Nishide, H. Polymer ,
1
0.345
0.345
0.341
0.335
0.330
0.324
3.14
3.15
3.13
3.12
3.10
3.08
110
110
109
108
106
105
0.0
0.0
0.9
1.8
3.6
4.5
2005, 46, 3767–3775.
20
40
60
80
100
a
12 Liang, F.; Kurata, T.; Nishide, H.; Kido, J. J Polym Sci Part A
Polym Chem 2005, 43, 5765–5773.
13 Tang, R.; Tan, Z.; Li, Y.; Xi, F. Chem Mater 2006, 18,
1053–1061.
14 Kim, Y.-H.; Zhao, Q.; Kwon, S.-K. J Polym Sci Part A Polym
Switching between 0 and 1.00 V (vs. Ag/AgCl).
Optical density change at 805 nm.
Ejected charge, determined from the in situ experiments.
Chem 2006, 44, 172–182.
b
c
15 Zhao, Q.; Kim, Y.-H.; Dang, T. T. M.; Shin, D.-C.; You, H.;
d
e
Coloration efficiency is calculated from the equation: g ¼ DOD/Q.
Kwon, S.-K.
341–347.
J Polym Sci Part A Polym Chem 2007, 45,
Decay of coloration efficiency after various cyclic scans.
experiments revealed that the introduction of the tert-butyl
group at the active sites of the TPA unit enhances the redox
and electrochromic stability of these polymers.
16 Su, H.-J.; Wu, F.-I.; Tseng, Y.-H.; Shu, C.-F. Adv Funct Mater
2005, 15, 1209–1216.
17 Wu, F.-I.; Yang, X.-H.; Neher, D.; Dodda, R.; Tseng, Y.-H.;
Shu, C.-F. Adv Funct Mater 2007, 17, 1085–1092.
CONCLUSIONS
18 Wu, F.-I.; Shih, P.-I.; Tseng, Y.-H.; Shu, C.-F.; Tung, Y.-L.;
A series of new polyamides 4a–f with tert-butyl-substituted
triphenylamine units were successfully prepared from 4-tert-
butyl-40,400-dicarboxytriphenylamine and various aromatic
diamines via the phosphorylation polyamidation reaction.
The polyamides exhibit good solubility and film-forming
capability and high thermal stability, and all of them are fluo-
rescent with blue-light emission. The polymers display very
well-defined and reversible redox processes in acetonitrile
solutions. Furthermore, they possess electrochomic behavior.
The polyamide 4f containing the tert-butyltriphenylamine
unit in both diacid and diamine components shows multi-
electrochromic behavior: colorless in the neutral state, green
in the semioxidized state, and purple in the fully oxidized
state. Good redox and electrochromic stability, moderate
fluorescence intensity, and proper HOMO values of these
polyamides make them promising candidates for optoelec-
tronic applications.
Chi, Y. J Mater Chem 2007, 17, 167–173.
19 Mikroyannidis, J. A.; Gibbons, K. M.; Kulkarni, A. P.;
Jenekhe, S. A. Macromolecules 2008, 41, 663–674.
20 Li, Y.; Xue, L.; Xia, H.; Xu, B.; Wen, S.; Tian, W. J Polym Sci
Part A Polym Chem 2008, 46, 3970–3984.
21 Vellis, P. D.; Mikroyannidis, J. A.; Cho, M. J.; Choi, D. H.
J Polym Sci Part A Polym Chem 2008, 46, 5592–5603.
22 Park, M. H.; Huh, J. O.; Do, Y.; Lee, M. H. J Polym Sci Part A
Polym Chem 2008, 46, 5816–5825.
23 Hsieh, B.-Y.; Chen, Y. J Polym Sci Part A Polym Chem 2009,
47, 1553–1566.
24 Jiang, Z.; Zhang, W.; Yao, H.; Yang, C.; Cao, Y.; Qin, J.; Yu,
G.; Liu, Y.
3651–3661.
J Polym Sci Part A Polym Chem 2009, 47,
25 Sim, J. H.; Kim, S. J.; Yamada, K.; Yokokyra, S.; Natori, I.;
Natori, S.; Sato, H. Synth Met 2009, 159, 85–90.
This work was supported by National Science Council of
Taiwan.
26 Park, M. H.; Yun, C.; Park, M. H.; Do, Y.; Yoo, S.; Lee, M. H.
Macromolecules 2009, 42, 6840–6843.
27 Cassidy, P. E. Thermally Stable Polymers; Marcel Dekker:
REFERENCES AND NOTES
New York, 1980.
1 Wienk, M. M.; Janssen, R. A. J. Chem Commun 1996,
28 Yang, H. H. Aromatic High-Strength Fibers; Wiley: New
267–268.
York, 1989.
2 Selby, T. D.; Blackstock, S. C. Org Lett 1999, 13, 2053–2055.
29 Oishi, Y.; Takado, H.; Yoneyama, M.; Kakimoto, M.;
3 Ito, A.; Ino, H.; Tanaka, K.; Kanemoto, K.; Kato, T. J Org
Imai, Y.
J Polym Sci Part A: Polym Chem 1990, 28,
Chem 2002, 67, 491–498.
1763–1769.
4 Selby, T. D.; Kim, K.-Y.; Blackstock, S. C. Chem Mater 2002,
30 Liou, G.-S.; Hsiao, S.-H.; Ishida, M.; Kakimoto, M.;
Imai, Y. Polym Sci Part A: Polym Chem 2002, 40,
2810–2818.
14, 1685–1690.
J
5 Murata, H.; Miyajima, D.; Nishide, H. Macromolecules, 2006,
39, 6331–6335.
31 Liou, G.-S.; Hsiao, S.-H. J Polym Sci Part A: Polym Chem
6 Tang, C. W.; VanSlyke, S. A. Appl Phys Lett 1987, 51, 913–915.
2003, 41, 94–105.
7 Adachi, C.; Nagai, K.; Tamoto, N. Appl Phys Lett 1995, 66,
32 Su, T.-H.; Hsiao, S.-H.; Liou, G.-S. J Polym Sci Part A: Polym
2679–2681.
Chem 2005, 43, 2085–2098.
2808
INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE
33 Liou, G.-S.; Hsiao, S.-H.; Su, T.-H. J Mater Chem 2005, 15,
41 Hsiao, S.-H.; Liou, G.-S.; Wang, H.-M. J Polym Sci Part A:
1812–1820.
Polym Chem 2009, 47, 2330–2343.
34 Hsiao, S.-H.; Chang, Y.-M.; Chen, H.-W.; Liou, G.-S. J Polym
42 Yen, H.-J.; Liou, G.-S. Chem Mater 2009, 21, 4062–4070.
Sci Part A: Polym Chem 2006, 44, 4579–4592.
43 Yang, C.-P.; Chen, R.-S.; Chen, K.-H. Colloid Polym Sci 2003,
35 Liou, G.-S.; Huang, N.-K.; Yang, Y.-L. Polymer 2006, 47,
281, 505–515.
7013–7020.
44 Yamazaki, N.; Matsumoto, M.; Higashi, F. J Polym Sci Part
36 Chang, C.-W.; Liou, G.-S.; Hsiao, S.-H. J Mater Chem 2007,
A: Polym Chem 1975, 13, 1373–1380.
17, 1007–1015.
45 Demas, J. N.; Crosby, G. A.
J Phys Chem 1971, 75,
37 Hsiao, S.-H.; Liou, G.-S.; Kung, Y.-C.; Yen, H.-J. Macromole-
991–1024.
cules 2008, 41, 2800–2808.
46 Yan, H.; Huang, Q.; Cui, J.; Veinot, G. C.; Kern, M. M.;
38 Chang, C.-W.; Yen, H.-J.; Huang, K.-Y.; Yeh, J.-M.; Liou,
Marks, T. J. Adv Mater 2003, 15, 835–838.
G.-S. J Polym Sci Part A: Polym Chem 2008, 46, 7937–7949.
47 Monk, P. M. S.; Mortimer, R. J.; Rosseinsky, D. R. Electro-
chromism and Electrochromic Devices, Cambridge University
Press: UK, 2007.
39 Lin, H.-Y.; Liou, G.-S. J Polym Sci Part A: Polym Chem 2009,
47, 285–294.
40 Liou, G.-S.; Lin, K.–H. J Polym Sci Part A: Polym Chem
48 Beaujuge, P. M.; Reynolds, J. R. Chem Rev 2010, 110,
2009, 47, 1988–2001.
268–320.
FLUORESCENT & ELECTROCHROMIC POLYAMIDES, HSIAO ET AL.
2809