Pyrenylamine-functionalized aromatic polyamides as efficient blue-emitters and multicolored electrochromic materials

Article abstract of DOI:10.1002/pola.24783

A series of novel aromatic polyamides with pyrenylamine in the backbone were prepared from a newly synthesized dicarboxylic acid monomer, N,N-di(4-carboxyphenyl)-1-aminopyrene, and various aromatic diamines via the phosphorylation polyamidation technique.

Full text of DOI:10.1002/pola.24783

Pyrenylamine-Functionalized Aromatic Polyamides as Efficient
Blue-Emitters and Multicolored Electrochromic Materials
YI-CHUN KUNG,1 SHENG-HUEI HSIAO2
1Department of Chemical Engineering, Tatung University, 40 Chungshan North Road, Third Section, Taipei 10452, Taiwan
2Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, Taipei 10608, Taiwan
Received 18 April 2011; accepted 17 May 2011
DOI: 10.1002/pola.24783
Published online 8 June 2011 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: A series of novel aromatic polyamides with
pyrenylamine in the backbone were prepared from a newly
synthesized dicarboxylic acid monomer, N,N-di(4-carboxy-
phenyl)-1-aminopyrene, and various aromatic diamines via the
phosphorylation polyamidation technique. These polyamides
were readily soluble in many organic solvents and could be
solution-cast into tough and amorphous films. They had useful
levels of thermal stability with glass-transition temperatures in
the range of 276–342 ꢀC and 10% weight loss temperatures in
excess of 500 ꢀC. The dilute N-methyl-2-pyrrolidone (NMP) sol-
utions of these polymers exhibited fluorescence maxima
around 455–540 nm with quantum yields up to 56.9%. The
polyamides also showed remarkable solvatochromism of the
emission spectra. Their films showed reversible electrochemi-
cal oxidation and reduction accompanied by strong color
changes from colorless neutral state to purple oxidized state
and to yellow reduced state. The polyamide 4g containing the
pyrenylamine units in both diacid and diamine sides exhibited
easily accessible p- and n-doped states, together with multicol-
C
V
ored electrochromic behaviors.
2011 Wiley Periodicals, Inc.
J Polym Sci Part A: Polym Chem 49: 3475–3490, 2011
KEYWORDS: cyclic voltammetry; electrochemistry; electro-
chromism; polyamides; pyrenylamine; redox polymers
In close enough proximity, an excited-state pyrene monomer
and ground-state monomer can form an excimer state that
fluoresces at a substantially longer wavelength than the
monomer emission. It has also been shown that the intensity
of the excimer emission can be enhanced by both inter- and
intramolecular aggregation of pyrene monomers due to a
greater probability of dimerization. The long fluorescence
lifetime, large Stokes shift, and tunable intensity of the exci-
mer make the pyrene unit a useful fluorophore labeling in
metal ion or nucleic acid probes.6 In recent years, pyrene
derivatives,7 polymers,8 starbursts,9 and dendrimers10 have
been reported in the context of organic electronic applica-
tions such as organic light-emitting devices (OLEDs), because
of their emissive properties combined with high charge car-
rier mobility. Although pyrene is a blue-emitting chromo-
phore, the use of pyrene as emitting materials in OLED
applications has been limited because of the aggregation
between planar pyrene molecules. The high tendency toward
p-stacking of the pyrene moieties generally lends the pyrene-
containing emitters strong intermolecular interactions in the
solid state, which leads to a substantial red shift of their flu-
orescence emission and a decrease of the fluorescence quan-
tum yields. Nonetheless, through molecular structure design,
the close packing/fluorescence quenching effect in pyrene-
type materials can be reduced or controlled. For example, a
successful effort in the prevention of p-stacking in small
INTRODUCTION Wholly aromatic polyamides (aramids) are
considered to be high-performance polymeric materials
because of their excellent thermal and oxidative stability, low
flammability, and superior mechanical properties.1 High-
modulus fibers of aramids were among the first high-
performance polymers to be commercialized.2 The most
R
important products were NomexV [poly(m-phenyleneisoph-
R
thalamide)] and KevlarV [poly(p-phenyleneterephthalamide)]
fibers commercialized by DuPont in the late 1960s. The stiff
polymer chains result not only in fibers with excellent me-
chanical properties but also in poor polymer solubility. The
limited solubility is attributed to the very small entropy
change during the dissolution process. The extremely high
transition temperatures of the commercial aramids and their
poor solubility in organic solvents lead to processing difficul-
ties and limit their applications. As a result, research efforts
have focused on enhancing their processability and solubility
to expand the scope of the technological applications of
these materials.3 In addition, there is currently a huge
research effort directed toward exploiting the special func-
tions of the polyamides by incorporating new chemical func-
tionalities in the main chain or in the lateral structure.4
Pyrene is one of the most useful fluorogenic units for fluo-
rescent sensors because it displays not only a well-defined
monomer emission but also an efficient excimer emission.5
Additional Supporting Information may be found in the online version of this article. Correspondence to: S.-H. Hsiao (E-mail: shhsiao@ntut.edu.tw)
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Journal of Polymer Science Part A: Polymer Chemistry, Vol. 49, 3475–3490 (2011) 2011 Wiley Periodicals, Inc.
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
molecules was achieved with 1,3,6,8-tetrasubstituted highly
sterically hindered pyrenes,11 which can emit blue light in
solution as well as in the solid state with a high efficient
yield. Additionally, diarylamino functionalized pyrene deriva-
tives have been found to efficiently perform as emitters and
charge transport materials in OLEDs.12
synthesis of pyrenylamine-containing polyamides from N,N-
di(4-aminophenyl)-1-aminopyrene and aromatic or aliphatic
dicarboxylic acids.23 It was found that the polyamides dis-
play reversible oxidation and reduction processes, indicating
their high electrochemical stability for both p- and n-doping
of the diphenylpyrenylamine (DPPA) core. These polyamides
also showed interesting fluorescent and electrochromic char-
acteristics. However, the emission color of the reported pyre-
nylamine-based polyamides red shifted to yellowish green,
and the quantum yield was not very high. This may be at-
tributable to a lower energy gap of the chromophoric sys-
tem. The reduced fluorescence quantum yield may also be
explained by the quenching effect from the charge-transfer
(CT) interactions between the pyrenylamine donor and the
aroyl acceptor. The results are consistent with that reported
by Kang and coworkers;24 they studied the emission color
tuning of 1,6-bis(N-phenyl-p-(R)-phenylamino)pyrenes and
found that large red-shifted fluorescence emissions and
lower quantum yields of the compounds are observed for R
¼ ANPh2 and ANMePh. They also demonstrated that the
electron-withdrawing substituents, such as R ¼ ACN and
AF, led to deep blue emission and much higher quantum
yields. In an attempt to obtain efficient blue-light-emitting
pyrenylamine-based polymers, herein, we synthesize N,N-
di(4-carboxyphenyl)-1-aminopyrene as a new dicarboxylic
acid monomer and its derived aromatic polyamides by direct
polycondensation with various aromatic diamines. The re-
sultant polyamides are expected to be good blue-emitters
with an enhanced fluorescence efficiency as compared
with their counterparts based on the previously reported
N,N-di(4-aminophenyl)-1-aminopyrene,23 because of the
decreased highest occupied molecular orbital (HOMO) level
and accordingly the increased energy gap together with the
reduced inter- and intramolecular CT interactions.
On the other hand, triarylamines are an important class of ar-
omatic compounds because they could form stable aminium
radical cations. Triarylamines can be building blocks for high
spin polyradicals that showed ferromagnetic coupling.13 Per-
haps most commonly, triarylamines have been used as the
hole-transport layer in electroluminescent devices,14,15 since
the two-layered organic electroluminescent device using a
bis(triphenylamine) as
a hole-transfer layer was first
reported by Tang and VanSlyke in 1987.16 Triarylamines can
be easily oxidized to form stable radical cations, and the oxi-
dation process is always associated with a noticeable change
of coloration. Thus, many triarylamine-based polymers have
been developed for potential electrochromic applications.17
In recent years, Liou and coworkers have developed several
high-performance polymers such as polyimides18 and poly-
amides19 carrying the triarylamine unit as a redox-chromo-
phore. The triarylamine-containing monomers such as
diamines and dicarboxylic acids could be easily prepared
using well-established procedures,20,21 and they could react
with the corresponding comonomers through conventional
polycondensation techniques, producing the desired triaryl-
amine-containing high-performance polymers. The polymers
have high glass-transition and decomposition temperature.
Because of the incorporation of packing-disruptive, propeller-
shaped triarylamine units along the polymer backbone, the
resulting polyamides generally exhibit good solubility in
many organic solvents. They could afford tough and flexible
films with good mechanical properties via simple solution
processing, which is advantageous for their ready fabrication
of large-area, thin-film devices. Thus, incorporation of three-
dimensional, packing-disruptive triarylamine units into the
polyamide backbone not only resulted in enhanced solubility
but also led to new electronic functions of polyamides, such
as electrochromic characteristics. The electrochromic function
of these polymers originates from the electroactive triaryl-
amine moieties, which can be reversibly oxidized as long as
the active sites of the aryl rings are protected. In addition,
these electrochromic polyamides are transparent at the neu-
tral state and can change to highly colorized at the oxidized
states. This electrochromic behavior is different from that of
the conjugated polymers extensively studied in recent
years.22 Most of the reported conjugated polymers to be used
as candidates for electrochromic applications are transparent
at their oxidized state. To get the electrochromic device trans-
missive, it must be continuously kept under potential which
may deteriorate the used polymers for fabrication in the time.
As our reported triarylamine-based polyamides are highly
transmissive at neutral state, it is safe to be used for this
application and away from such possible deterioration.
EXPERIMENTAL
Materials
The starting material of 1-aminopyrene (mp: 115–116 ꢀC)
was synthesized by the electrophilic nitration of copper
nitrate, followed by hydrazine Pd/C-catalytic reduction of
intermediate nitro compound according to a previously
reported procedure.23 4-Fluorobenzonitrile (TCI), cesium flu-
oride (CsF; Acros), and triphenyl phosphite (TPP; Acros)
were used without further purification. N,N-Dimethylaceta-
mide (DMAc; Tedia), N,N-dimethylformamide (DMF; Tedia),
pyridine (Py; Tedia), and N-methyl-2-pyrrolidone (NMP;
Tedia) were dried over calcium hydride for 24 h, distilled
under reduced pressure, and stored over 4 Å molecular
sieves in a sealed bottle. p-Phenylenediamine (3a; TCI) and
9,9-bis(4-aminophenyl)fluorene (3e; TCI) were purified by
sublimation in vacuo and recrystallization from ethanol,
respectively. m-Phenylenediamine (3b; Acros), 4,40-oxydiani-
line (3c; TCI), and 2,2-bis(4-aminophenyl)hexafluoropropane
(3d; TCI) were used as received. 20,50-Bis(4-amino-2-trifluoro-
25
ꢀ
methylphenoxy)-p-terphenyl (3f; mp: 222–223 C) and N,N-
di(4-aminophenyl)-1-aminopyrene (3g; mp: 227–229 ꢀC)23
were synthesized by the procedures reported previously.
In view of the attractive properties associated with the py-
rene and triarylamine units, we have recently reported the
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ARTICLE
Commercially obtained anhydrous calcium chloride (CaCl2)
was dried under vacuum at 180 ꢀC for 8 h before use.
Tetrabutylammonium perchlorate (TBAClO4; TCI) was recrys-
tallized twice by ethyl acetate under nitrogen atmosphere
and then dried in vacuo before use. Poly(methyl methacry-
late) [PMMA; weight-average molecular weight (Mw)
120,000] and propylene carbonate (PC) were used as
received from Aldrich and Acros Organic, respectively. All
other reagents were used as received from commercial
sources.
filtered while hot and cooled to room temperature, and the
pH value of filtrate was adjusted to near 3 by 3 M hydro-
chloric acid (HCl). The yellow precipitate was filtered,
washed thoroughly with water, and recrystallized from acetic
acid/water to afford 3.86 g (88.5% in yield) oꢀf pale yellow
ꢀ
needles with a mp of 312–314 C (by DSC at 5 C/min).
FTIR (KBr): 2700–3200 cmꢁ1 (OAH stretch), 1682 cmꢁ1
(C¼¼O stretch). 1H NMR (500 MHz, DMSO-d6, d, ppm): 7.11
(d, J ¼ 8.8 Hz, 4H, Hj), 7.86 (d, J ¼ 8.8 Hz, 4H, Hk), 7.96 (d, J
¼ 8.1 Hz, 1H, Ha), 7.99 (d, J ¼ 9.3 Hz, 1H, Hd), 8.11 (t, J ¼
7.6 Hz, 1H, Hf), 8.15 (d, J ¼ 9.3 Hz, 1H, Hc), 8.25 (d, J ¼ 9.1
Hz, 1H, Hi), 8.27 (d, J ¼ 9.1 Hz, 1H, Hh), 8.28 (d, J ¼ 7.5 Hz,
1H, He), 8.37 (d, J ¼ 7.6 Hz, 1H, Hg), 8.43 (d, J ¼ 8.2 Hz, 1H,
Hb). 13C NMR (125 MHz, DMSO-d6, d, ppm): 120.82 (C18),
121.96 (C6), 123.82 (C4), 124.20 (C20), 125.47 (C14), 125.64
(C8), 125.91 (C10), 126.64 (C3), 126.80 (C9), 127.18 (C13),
127.74 (C12), 127.76 (C15), 127.92 (C2), 128.80 (C5), 130.13
(C16), 130.34 (C11), 130.63 (C7), 131.06 (C19), 138.41 (C1),
150.73 (C17), 166.79 (C¼¼O). Anal. Calcd (%) for C30H19NO4
(457.48): C, 78.76%; H, 4.19%; N, 3.06%. Found: C, 77.82%;
H, 4.23%; N, 3.09%.
Synthesis of N,N-Di(4-cyanophenyl)-1-aminopyrene (1)
To a solution of 15.20 g (70 mmol) of 1-aminopyrene and
17.56 g (145 mmol) of 4-fluorobenzonitrile in 100 mL of
dried dimethyl sulfoxide (DMSO), 22.79 g (150 mmol) of
dried CsF was added with stirring all at once, and the mix-
ture was heated at 170 ꢀC for 18 h under nitrogen atmos-
phere. The mixture was poured into 1 L of water/methanol
(1:1). The precipitated compound was collected by filtration
and washed thoroughly by methanol and hot water. The
crude product was filtered and recrystallized from acetic
acid/water to afford 20.55 g (70% in yield) of pale brown
needles with an mp of 241–242 ꢀC (by ꢀdifferential scanning
calorimetry (DSC) at a heating rate of 5 C/min).
FTIR (KBr): 2218 cmꢁ1 (CBN stretch). 1H NMR (500 MHz,
DMSO-d6, d, ppm): 7.16 (d, J ¼ 8.8 Hz, 4H, Hj), 7.70 (d, J ¼
8.8 Hz, 4H, Hk), 7.82 (d, J ¼ 9.2 Hz, 1H, Ha), 7.98 (d, J ¼ 8.2
Hz, 1H, Hd), 8.13 (t, J ¼ 7.7 Hz, 1H, Hf), 8.18 (d, J ¼ 9.3 Hz,
1H, Hb), 8.27 (d, J ¼ 9.0 Hz, 1H, Hi), 8.30 (d, J ¼ 9.0 Hz, 1H,
Hh), 8.31 (d, J ¼ 7.2 Hz, 1H, He), 8.39 (d, J ¼ 7.6 Hz, 1H, Hg),
8.44 (d, J ¼ 8.2 Hz, 1H, Hc). 13C NMR (125 MHz, DMSO-d6, d,
ppm): 104.19 (C20), 118.94 (CBN), 121.57 (C18 þ C2),
123.72 (C4), 125.41 (C14), 125.84 (C8), 126.12 (C10), 126.71
(C5), 126.90 (C9), 127.13 (C13), 127.75 (C15), 127.90 (C6),
128.08 (C12), 129.22 (C3), 130.28 (C16), 130.54 (C11), 130.57
(C7), 133.81 (C19), 137.19 (C1), 150.13 (C17). Anal. Calcd (%)
for C30H17N3 (419.48): C, 85.90%; H, 4.08%; N, 10.02%.
Found: C, 85.77%; H, 4.12%; N, 10.11%.
Synthesis of Polyamides
The synthesis of polyamide 4a was used as an example to
illustrate the general synthetic route. A mixture of 0.421 g
(0.92 mmol) of diacid monomer (2), 0.100 g (0.92 mmol) of
p-phenylenediamine (3a), 0.1 g of calcium chloride, 1.0 mL
of TPP, 0.4 mL of pyridine, and 1.5 mL of NMP was heated
with stirring at 120 ꢀC for 3 h. The obtained polymer solu-
tion was poured slowly into 200 mL of stirred methanol giv-
ing rise to a stringy, fiber-like precipitate that was collected
by filtration, washed thoroughly with hot water and metha-
nol, and dried under vacuum at 100 ꢀC. Reprecipitations of
the polymer by DMAc/methanol were carried out twice for
further purification. The inherent viscosity of the obtained
polyamide 4a was 0.85 dL/g, measurꢀed at a concentration of
0.5 g/dL in 5 wt % LiCl DMAc at 30 C.
FTIR (film): 3311 (amide NAH stretch), 1649 cmꢁ1 (amide
C¼¼O stretch). 1H NMR (500 MHz, DMSO-d6, d, ppm): 7.13
(d, J ¼ 8.2 Hz, 4H, Hj), 7.68 (s, 4H, Hl), 7.89 (d, J ¼ 8.2 Hz,
4H, Hk), 7.96 (d, J ¼ 7.9 Hz, 1H, Ha), 8.04 (d, J ¼ 9.3 Hz, 1H,
Hc), 8.12 (t, J ¼ 8.2 Hz, 1H, Hf), 8.15 (d, J ¼ 9.2 Hz, 1H, Hd),
8.25 (s, 2H, Hi þ Hh), 8.27 (d, J ¼ 7.7 Hz, 1H, He), 8.35 (d, J
¼ 7.2 Hz, 1H, Hg), 8.42 (d, J ¼ 7.7 Hz, 1H, Hb), 10.09 (s, 2H,
amide NAH).
Synthesis of N,N-Di(4-carboxyphenyl)-1-aminopyrene (2)
A mixture of 5.35 g (95 mmol) of potassium hydroxide and
4.00 g (9.5 mmol) of the obtained dinitrile compound 1 in
30 mL of ethanol and 40 mL of distillated water was stirred
at 110 C until no further ammonia was generated. The time
taken to reach this stage was about 4 days. The solution was
ꢀ
PYRENYLAMINE-FUNCTIONALIZED AROMATIC POLYAMIDES, KUNG AND HSIAO
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
side of the electrode, and the electrodes were sandwiched.
Finally, an epoxy resin was used to seal the device.
Measurements
Infrared spectra were recorded on a Horiba FT-720 FT-IR
spectrometer. Elemental analyses were run in a Heraeus Var-
ioEL-III CHNS elemental analyzer. 1H and 13C NMR spectra
were measured on a Bruker AVANCE-500 FT-NMR using tet-
ramethylsilane as the internal standard. The inherent viscos-
ities were determined at 0.5 g/dL concentration using Can-
non-Fenske viscometer at 30 ꢀC. Mw and number-average
molecular weights (Mn) were obtained via gel permeation
chromatography (GPC) on the basis of polystyrene calibra-
tion using Waters 2410 as an apparatus and tetrahydrofuran
(THF) as the eluent. Wide-angle X-ray diffraction (WAXD)
measurements were performed at room temperature (ca. 25
ꢀC) on a Shimadzu XRD-6000 X-ray diffractometer (40 kV, 20
mA), using graphite-monochromatized Cu-Ka radiation. Ther-
mogravimetric analysis (TGA) was conducted with a Perki-
nElmer Pyris 1 TGA. Experiments were carried out on ꢃ3–5
mg film samples heated in flowing nitrogen or air (flow rate
Preparation of the Polyamide Films
A solution of polymer was made by dissolving about 0.5 g of
the aramid sample in 10 mL of DMAc. The homogeneous so-
lution was poured into a 9-cm glass Petri dish, which was
placed in a 90 ꢀC oven for 5 h to remove most of the sol-
vent;ꢀ then, the semidried film was further dried in vacuo at
180 C for 8 h. The obtained films were about 70–90 lm in
thickness and were used for X-ray diffraction measurements,
solubility tests, and thermal analyses.
3
ꢀ
¼ 20 cm /min) at a heating rate of 20 C/min. DSC analyses
Fabrication of Electrochromic Device
were performed on a PerkinElmer Pyris 1 DSC at a scan rate
3
ꢀ
Electrochromic polymer films were prepared by dropping sol-
utions of the aramids (4 mg/mL in DMAc) onto an indium tin
oxide (ITO)-coated glass substrate (20 ꢂ 30 ꢂ 0.7 mm3, 50–
100 X/square). The polymers were drop-coated onto an active
area of letters TTU using a mask. A gel electrolyte based on
PMMA (Mw: 120,000) and LiClO4 was plasticized with PC to
form a highly transparent and conductive gel. The gel electro-
lyte was prepared as follows. PMMA (3 g) was dissolved in
dry acetonitrile (15 g), and LiClO4 (0.3 g) was added to the
polymer solution as supporting electrolyte. Then, PC (5 g) was
added as plasticizer. The mixture was then slowly heated until
gelation. The gel electrolyte was spread on the polymer-coated
of 20 C/min in flowing nitrogen (20 cm /min). Thermome-
chanical analysis (TMA) was conducted with a PerkinElmer
TMA 7 instrument. The TMA experimeꢀnts were conducted
ꢀ
from 50 to 350 C at a scan rate of 10 C/min with a pene-
tration probe 1.0 mm in diameter under an applied constant
load of 10 mN. Softening temperatures (Ts) were taken as
the onset temperatures of probe displacement on the TMA
traces. Absorption spectra were measured with an Agilent
8453 UV–visible diode array spectrophotometer. Fluores-
cence (FL) spectra were measured with a Varian Cary Eclipse
fluorescence spectrophotometer. Fluorescent quantum yield
was determined using solutions in NMP and was calculated
SCHEME 1 Synthetic route to the
diacid monomer 2.
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ARTICLE
FIGURE 1 (a) 1H, (b) 13C, (c) HAH COSY, and (d) CAH HMQC NMR spectra of the target diacid monomer 2 in DMSO-d6.
SCHEME 2 Synthesis of polyamides.
PYRENYLAMINE-FUNCTIONALIZED AROMATIC POLYAMIDES, KUNG AND HSIAO
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 1 Inherent Viscosity and Solubility Behavior of
Polyamides
Solubility in Various Solventsb
a
Polymer ginh
Code
(dL/g) NMP DMAc DMF DMSO m-Cresol THF
4a
4b
4c
4d
4e
4f
0.85
0.49
0.77
0.38
0.50
0.52
0.68
1.09
0.48
1.11
0.49
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
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þþ
þ
þꢁ
þꢁ
þꢁ
þþ
þꢁ
þþ
þꢁ
ꢁ
þ
þ
þþ
þ
þþ
þ
4g
5ac
5b
5c
5e
a
þ
þ
ꢁ
þ
ꢁ
ꢁ
FIGURE 2 TGA and DSC (inset) curves of polyamide 4g with a
heating rate of 20 ꢀC/min. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
þ
Inherent viscosity measured at a concentration of 0.5 dL/g in DMAc–5
wt % LiCl at 30 ꢀC.
b
Solubility: þþ, soluble at room temperature; þꢁ, partially soluble; þ,
RESULTS AND DISCUSSION
soluble on heating; and ꢁ, insoluble even on heating. Solvent: NMP, N-
methyl-2-pyrrolidone; DMAc, N,N-dimethylacetamide; DMF, N,N-dime-
thylformamide; DMSO, dimethyl sulfoxide; and THF, tetrahydrofuran.
Monomer Synthesis
As shown in Scheme 1, the new pyrenylamine-based dicar-
boxylic acid monomer named as N,N-di(4-carboxyphenyl)-
1-aminopyrene (2) was successfully synthesized by the
CsF-assisted N,N-diarylation reaction of 1-aminopyrene with
4-fluorobenzonitrile in DMSO, followed by the alkaline hydro-
lysis of the intermediate dicyano compound 1 and the acidifi-
cation of the resulting potassium carboxylate. Elemental and
c
Structurally related polyamides with the corresponding Ar residue as
in the 4 series analogs:
TABLE 2 Thermal Properties of Polyamidesa
Td at 10 wt %
by comparing emission with that of a standard solution of
9,10-diphenylanthracene in cyclohexane (UFL ¼ 90%) at
room temperature. Electrochemistry was performed with a
CH Instruments 611C electrochemical analyzer. Cyclic vol-
tammetry (CV) was conducted with the use of a three-
electrode cell in which ITO (polymer film area ca. 1 cm2, 0.8
ꢂ 1.25 cm2) was used as a working electrode. A platinum
wire was used as an auxiliary electrode. All cell potentials
were taken with the use of at a home-made Ag/AgCl, KCl
(sat.) reference electrode. Ferrocene was used as an external
reference for calibration (þ0.44 V vs. Ag/AgCl). Voltammo-
grams are presented with the positive/negative potential
pointing to the right/left with increasing anodic/decreasing
cathodic current pointing upward/downward. Spectroelectro-
chemistry analyses were carried out with an electrolytic cell,
which was composed of a 1-cm cuvette, ITO as a working
electrode, a platinum wire as an auxiliary electrode, and a
Ag/AgCl reference electrode. Absorption spectra in the spec-
troelectrochemical experiments were also measured with an
Agilent 8453 UV–visible diode array spectrophotometer. A
model HCPS-03-0310 laboratory Pulse Power Supply was
used as the direct current power source to fix the potential
between the two ITO electrodes of the device. Color mea-
surements were performed by using Konica Minolta CS-100A
ChromaMeter with viewing geometry as recommended by
Commision Internationale de I’Eclairage.
Lossd (ꢀC)
Char
Tg
Ts
Yielde
(%)
b
c
Index
(ꢀC)
(ꢀC)
In N2
In Air
4a
4b
4c
4d
4e
4f
313
295
295
306
342
276
312
293
271
280
316
311
289
294
305
322
269
314
288
270
277
318
553
530
529
512
540
531
576
496
505
495
538
542
526
544
518
523
502
574
513
512
496
540
79
78
73
70
76
70
78
70
74
67
66
4g
5a
5b
5c
5e
a
The polymer film samples were heated at 300 ꢀC for 1 h before all the
thermal analyses.
b
The sample were heated from 50 to 400 ꢀC at a scan rate of 20 ꢀC/min
followed by rapid cooling to 50 ꢀC at ꢁ200 ꢀC/min in nitrogen. The mid-
point temperature of baseline shift on the subsequent DSC trace (from
50 to 400 ꢀC at heating rate 20 ꢀC/min) was defined as Tg.
c
Softening temperature measured by TMA using a penetration method.
d
Decomposition temperature at which a 10% weight loss was recorded
by TGA at a heating rate of 20 ꢀC/min.
e
Residual weight percentages at 800 ꢀC under nitrogen flow.
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ARTICLE
signals of C20 adjacent to the cyano or carboxyl group. The
C20 of dicyano compound 1 resonated at a higher field (104.2
ppm) than the other aromatic carbons due to the anisotropic
shielding by the cyano p-electrons. After hydrolysis, the reso-
nance peak of C20 shifted to a lower field (124.2 ppm)
because of the lack of an anisotropic field. Thus, the spectro-
scopic data convincingly prove the successful synthesis of the
target dicarboxylic acid monomer.
TABLE 3 Absorption and Fluorescent Properties of Polyamides
In Solutionb
As Solid Film (nm)
c
kem
UFL
Indexa kabs (nm)
(nm) (%)d k0
kabs konset kem
c
4a
4b
4c
4d
4e
4f
362, 334 sh 458
33.0 426 363 431
465
462
464
465
463
465
522
355, 334 sh 458
353, 334 sh 458
356, 334 sh 455
353, 334 sh 458
355, 331 sh 455
48.4 428 358 430
52.3 430 355 435
53.5 423 358 428
56.4 426 355 433
56.9 424 358 428
16.9 448 369 452
1.2 458 335 469
25.0 457 336 465
26.1 456 336 467
8.8 455 334 461
0.8 406 361 408
7.7 404 361 405
2.0 411 361 414
10.4 408 360 412
Polymer Synthesis
According to the phosphorylation polyamidation technique
described by Yamazaki et al.,26 a series of novel aromatic
polyamides 4a–4g with main-chain DPPA units were synthe-
sized from the dicarboxylic acid monomer 2 with various
aromatic diamines 3a–3g via solution polycondensation
using TPP and pyridine as condensing agents (Scheme 2).
Diamines 3a–e were obtained from commercial sources,
whereas diamines 3f and 3g were synthesized according to
the reported procedures.23,25 All the polymerization reac-
tions proceeded homogeneously throughout the reaction
and gave clear and highly viscous polymer solutions. The
products precipitated in a tough, fiber-like form when the
resulting polymer solutions were slowly poured into stirring
methanol. As shown in Table 1, the obtained polyamides
had inherent viscosities in the range of 0.48–0.85 dL/g. The
transparent and tough films can be obtained through solu-
tion-casting process which indicated the moderate to high
molecular weight polyamides were achieved. For a compara-
tive purpose, four structurally related polyamides 5a–c and
5e (see the footnote in Table 1) were also prepared from
4,40-dicarboxytriphenylamine with the corresponding aro-
matic diamines in a similar synthetic procedure as that
used for the 4 series polyamides. The molecular weight
data of THF-soluble polyamides 4d and 4f were measured
by GPC using polystyrenes as standard with THF as solvent.
The Mw of polymers 4d and 4f were 32,500 and 45,000
with polydispersity index (Mw/Mn) of 2.03 and 1.88, respec-
tively. The structures of the polyamides could be affirmed
by IR and NMR spectroscopy. Supporting Information Figure
S3 shows a typical IR spectrum for polyamide 4a. The char-
acteristic IR absorption bands of the amide group appeared
at around 3311 cmꢁ1 (NAH stretch) and 1649 cmꢁ1 (amide
carbonyl). Supporting Information Figure S4 shows a typical
set of 1H and two-dimensional HAH COSY spectra of poly-
amide 4a in DMSO-d6. All the resonance peaks could be
readily assigned to the hydrogen atoms in the repeating
unit. The resonance signal appearing at 10.1 ppm in the 1H
NMR spectrum also supports the formation of amide
linkages.
4g
40a
40b
40c
40d
5a
5b
5c
5e
a
370, 335
540
e
335, 385 sh 525
335, 412 sh 533
335, 371 sh 536
335, 412 sh 531
–
509
509
513
–
364
355
355
355
419
421
420
422
453
455
452
Analogous polyamides 40 having the corresponding isomeric repeat
unit as those of the 4 series ones.
b
The polymer concentration was 10ꢁ5 mol/L in NMP.
c
Excited at the absorption maximum for both the solid and solution
states.
d
The fluorescent quantum yield was calculated in an integrating sphere
with 9,10-diphenylanthracene as the standard (UFL ¼ 90%).
e
Difficult to be defined because of low fluorescence intensity.
spectroscopic analyses were used to identify structures of the
intermediate dicyano compound 1 and the target dicarboxylic
acid monomer 2. The FTIR spectra of the synthesized com-
pounds are illustrated in the Supporting Information Figure
S1. The cyano groups of compound 1 gave characteristic
bands at 2218 cmꢁ1. After hydrolysis, the characteristic
absorptions of the cyano group disappeared, and the carbox-
ylic acid group showed the typical C¼¼O and OAH stretching
absorptions at 1682 and 2700–3200 cmꢁ1, respectively. The
NMR data of the intermediate dicyano compound 1 are
included in the Supporting Information Figure S2. The 1H,
13C, HAH COSY, and CAH HMQC NMR spectra of the target
diacid monomer 2 are compiled in Figure 1. Assignments of
each carbon and proton are also indicated in these spectra,
and they are in good agreement with the proposed structures
of these two compounds. The 13C NMR spectra confirm that
the cyano groups were completely transformed into the car-
boxylic acid groups by the disappearance of the resonance
peak for the cyano carbon at 118.9 pm and the appearance
of the carbonyl peak at 166.8 pm. Other important evidence
of this transformation is the shifting of the carbon resonance
Solubility and Film Property
The solubility behaviors of polyamides 4a–4g are also pre-
sented in Table 1. All the polymers were readily dissolved
in highly polar organic solvents such as NMP, DMAc, DMF,
and DMSO, attributed mainly to the introduction of bulky,
three-dimensional DPPA unit into the polymer backbone.
Polyamides 4d and 4f also showed good solubility in less
polar solvents such as THF because of the additional contri-
bution of the bulky trifluoromethyl (ACF3) groups and
PYRENYLAMINE-FUNCTIONALIZED AROMATIC POLYAMIDES, KUNG AND HSIAO
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 3 Normalized UV–vis absorption and fluorescence spectra of all polyamides with a concentration of 10ꢁ5 M in NMP. The
fluorescence photographs of their NMP solutions and solid films (ca. 0.2 lm) were taken under illumination of a 365 nm UV light.
laterally attached p-terphenyl segment. Thus, the excellent
solubility makes these polymers potential candidates for
practical applications by simple solution processing to afford
high-performance thin films for optoelectronic devices. The
WAXD studies of these film samples indicated that all the
polymers are essentially amorphous due to the presence of
packing-disruptive DPPA units (see Supporting Information
Figure S5).
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FIGURE 4 UV–vis absorption and fluorescence spectra of aramids 4c and 40c with a concentration of 10ꢁ5 M in NMP. The fluores-
cence photographs of their NMP solutions and solid films (ca. 0.2 lm) were taken under illumination of a 365 nm UV light. [Color
figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
Thermal Properties
referred as apparent Tg) of the polymer films were deter-
mined by the TMA method using a loaded penetration probe.
They were read from the onset temperature of the probe
displacement on the TMA trace. The Ts values are also listed
in Table 2. In most cases, the Ts values of these polyamides
obtained by TMA are comparable to the Tg values measured
by the DSC experiments. The thermal analysis results reveal
that these polyamides exhibit high thermal stability, which in
turn is beneficial to increase the operational lifetime in de-
vice application and enhance the morphological stability to
the solution-processed films.
The thermal stability and transition temperatures of the
polyamides were investigated by TGA, DSC, and TMA techni-
ques. A typical set of TGA and DSC curves of the representa-
tive polyamide 4g are shown in Figure 2, and the thermal
data of all polyamides are summarized in Table 2. These pol-
yamides show a high thermal stability; there is no obvious
ꢀ
weight loss before the scanning temperature reaches 450 C
in nitrogen or in air. Their decomposition temperatures (Td)
at a 10% weight loss in nitrogen and air were recorded at
504–576 ꢀC and 502–577 ꢀC, respectively. The amount of
carbonized residue (char yield) of these polymers was more
than 68% at 800 ꢀC in nitrogen atmosphere. The high char
yields of these polymers can be ascribed to their high aro-
matic content. The glass-transition temperatures (Tg) of the
4 series polyamides were observed in the range of 276–313
ꢀC by DSC. The lowest Tg value (276 ꢀC) of 4f can be
explained in terms of the decreased rotation barrier caused
by the flexible ether linkages together with the increased
free volume due to bulky pendent trifluoromethyl groups
and the laterally attached p-terphenyl structure in the dia-
mine component. As compared with the 5 series analogs, the
present series polyamides exhibit an increased Tg as a result
of the presence of rigid pyrene units. The Ts (may be
Absorption and Fluorescence Properties
The UV–vis absorption and fluorescence spectra of the polya-
mides were measured in dilute NMP solutions (ꢃ1 ꢂ 10ꢁ5
mol/L) and as thin solid films, and the pertinent data are
presented in Table 3. As shown in Figure 3, the absorption
maxima of polyamides 4a–4f lie in the range of 353–362 nm
primarily because of the p–p* transition and n–p* transitions
of the conjugated aromatic segments. Their emission maxima
were at around 455–458 nm in the blue region with fluores-
cence quantum yields (UFL) ranging from 33.0 to 56.9%.
When compared with the corresponding 5 series counter-
parts, the higher quantum efficiency of the present series
PYRENYLAMINE-FUNCTIONALIZED AROMATIC POLYAMIDES, KUNG AND HSIAO
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
3. Obviously, all the 4 series polymers revealed a shorter
wavelength emission and a higher fluorescence yield com-
pared with the corresponding 40 counterparts. For a clearer
comparison, the absorption and fluorescence spectra to-
gether with the fluorescence images of polyamides 4c and
40c are illustrated in Figure 4. For the referenced polyamide
40c, the absorption band at around 336 nm is attributed to
p–p* and n–p* transitions of the conjugated aromatic seg-
ments, and that at longer wavelength (400–450 nm) may be
assigned to inter- or intramolecular CT transitions from the
DPPA donor to the benzoyl acceptor. The primary absorption
band of polyamide 4c shifted to a longer wavelength
(ꢃ355 nm) as compared with 40c, which can be due to reso-
nance interactions in the para amino-substituted benzoyl
structure in the polymer backbone of 4c. The solution fluo-
rescence peak wavelength (kem) of 4c is located at 458 nm,
and its full width at half maximum (FWHM) is 59 nm, which
is about 40 nm smaller than 40c (kem ¼ 536 nm, FWHM ¼
98 nm). Polyamide 4c is a blue light emitter in both solution
and solid states, whereas 40c is a yellowish-green or green
light emitter. The quantum yield of 40c is much lower than
that of 4c, possibly because of CT quenching. Thus, by chang-
ing the amide (ACONHA) orientation in these polyamide
chains, it is possible to achieve the desired emission in the
deep blue region of the visible spectrum with an enhanced
quantum yield.
In contrast to absorption spectra, a strong medium effect is
observed in the fluorescence spectra of these polyamides.
For example, the absorption and PL spectra of the dilute sol-
utions of polyamide 4f in different solvents are illustrated in
Figure 5. The emission maximum kem of 4f in THF, NMP, and
DMSO and its solid film appeared at 436, 455, 461, and 465
nm, respectively. The kem value increases as the solvent
polarity increases. This clearly indicates that the polyamide
stabilized in the excited state by the polar solvent molecules
will display red-shifted emission. The large solvatochromism
of the emission spectra also indicates that these polyamides
permit strong intramolecular CT from the donor (pyrenyl-
amine) to the acceptor (benzoyl).
FIGURE 5 Normalized UV–vis absorption and fluorescence
spectra of the dilute solution of polyamide 4f (ca. 10ꢁ5 M). Pho-
tographs were taken under illumination of a 365 nm UV light.
[Color figure can be viewed in the online issue, which is avail-
able at wileyonlinelibrary.com.]
polyamides could be attributable to the presence of rigid,
highly fluorescent pyrene chromophore. The spectral shifts
in both absorption and fluorescence are very limited, indicat-
ing very small electronic perturbation of the Ar group in
polyamides 4a–f. In the solid state, 4a–f showed similar
absorption profiles as those measured in solution, with
absorption maxima centered at 355–363 nm with absorption
onset at 428–435 nm corresponding to optical bandgaps of
2.85–2.90 eV. As the photographs shown in Figure 3, 4a–f in
both solution and solid states showed strong blue fluores-
cence, suggesting that they are promising blue-emitting
materials.
Electrochemical Properties
The electrochemical behavior of these polyamides was inves-
tigated by CV conducted for the cast films on an ITO-coated
glass substrates working electrode in dry acetonitrile
(CH3CN; for anodic oxidation) or DMF (for cathodic reduc-
tion) containing 0.1 M of TBAClO4 as an electrolyte and
saturated Ag/AgCl as reference electrode under nitrogen
atmosphere. The derived oxidation and reduction potentials
are summarized in Table 4. Figure 6(a) depicts the CV curve
for polyamide 4c, which is representative for the other 4a–f
analogs. Polymers 4a–f displayed a reversible reduction pro-
cess at E1/2 [(Epa þ Epc)/2] ¼ ꢁ1.88 to ꢁ1.90 V and an irre-
versible oxidation process at Eonset ¼ 1.00–1.02 V. The
anodic wave originates from the oxidation of the DPPA seg-
ment, and the cathodic wave is attributable to the reduction
of the pyrene group. The polyamide 4g exhibits the DPPA
segment in both diacid and diamine components and displays
an additional anodic oxidation wave at E1/2 ¼ 0.82 V [Fig.
Different from 4a–f, polyamide 4g containing the pyrenyl-
amine unit in both the diacid and diamine components
showed a red-shifted absorption and emission together with
a relatively lower quantum yield (UFL ¼ 16.9%). Yellowish-
green fluorescent polyamide 4g had a lower quantum yield
consistent with the energy gap law.27 The fluorescent prop-
erties of polyamide 4g is similar to those reported for the 40
series analogs based on the previously reported N,N-di(4-
aminophenyl)-1-aminopyrene.23 For comparison, the previ-
ously reported absorption and fluorescence data of four pol-
yamides (40a–d) with an isomeric repeating unit to that of
the corresponding polyamides 4a–d are also listed in Table
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TABLE 4 Redox Potentials and Energy Levels of Polyamides
Oxidation
Potential (V)a
Reduction Potential (V)b
Eogpt
(eV)c
ECgV
(eV)d
EHOMO/LUMO
(eV)e
ox
E
red
onset
red
Index
E
E
1=2
onset
4a
4b
4c
4d
4e
4f
1.00
1.02
1.01
1.01
1.02
1.01
0.71
0.69
0.68
0.68
0.70
1.02
1.02
1.03
1.02
ꢁ1.78
ꢁ1.77
ꢁ1.76
ꢁ1.78
ꢁ1.76
ꢁ1.74
ꢁ1.72
ꢁ1.82
ꢁ1.80
ꢁ1.84
ꢁ1.77
–
ꢁ1.90
ꢁ1.89
ꢁ1.88
ꢁ1.89
ꢁ1.88
ꢁ1.90
ꢁ1.90, ꢁ1.99f
ꢁ2.02
ꢁ1.98
ꢁ2.05
ꢁ2.04
–
2.88
2.88
2.85
2.90
2.86
2.90
2.74
2.64
2.67
2.66
2.69
3.04
3.06
3.00
3.01
2.78
2.79
2.77
2.79
2.78
2.76
2.43
2.51
2.48
2.52
2.47
–
5.36/2.58
5.38/2.59
5.37/2.60
5.37/2.58
5.38/2.60
5.37/2.61
5.07/2.64
5.05/2.54
5.04/2.56
5.04/2.52
5.06/2.59
5.38/2.34
5.38/2.32
5.39/2.39
5.38/2.37
4g
40a
40b
40c
40d
5a
5b
5c
5e
a
–
–
–
–
–
–
–
–
–
Versus Ag/AgCl in CH3CN.
b
c
Versus Ag/AgCl in DMF. Er1e=d2: average potential of the redox couple peaks.
The data were calculated from polymer films by the equation: Eogpt ¼ 1240/konset (optical energy gap
between HOMO and LUMO).
d
Bandgap calculated from CV measurement.
e
ox
onset
red
The HOMO and LUMO energy levels were calculated from E
and E
values of CV curves and were
onset
referenced to ferrocene (4.8 eV relative to the vacuum energy level).
f
The values were determined by DPV measurements.
6(b)]. This oxidation process starting at about 0.71 V is re-
versible, indicating that the DPPA segment in the diamine
residue could form a stable radical cation due to its more
electron-rich nature. The second (Epa ¼ 1.5 V) oxidation peak
is related the electron loss from the DPPA segment in the
diacid component of polyamide 4g. Additionally, the cathodic
reduction wave originating from the pyrene unit corresponds
to a two-electron charging event because 4g contains the
DPPA segment in both diacid and diamine residues. From the
differential pulse voltammogram (DPV) of 4g shown in Figure
7(a) and the CV curves of the diamide model compounds M1
and M2 shown in Figure 7(b), we believe that the first reduc-
tion peak at Epc ¼ ꢁ1.85 V appears to involve one electron
charged into the pyrene unit of the diacid component, and
the second reduction peak at Epc ¼ ꢁ1.96 V arises from the
second electron charged into the pyrene unit of the diamine
component. However, these two reduction processes occurred
almost simultaneously at the CV scan rate we used. There-
fore, these two reduction waves merged and became in-
distinguishable in the CV diagram. Furthermore, a linear
dependence of the peak currents as a function of scan rates
confirmed both a nondiffusional redox process and a well-
adhered electroactive polymer film [Fig. 7(c,d)]. Because of
the stability of the films and good adhesion between the
polymer and ITO-glass substrate, 4g exhibited good redox
stability during the first oxidation process.
On the basis of the oxidation and reduction onset potentials,
the bandgaps for polyamides 4a–4f were calculated, and were
found to vary from 2.76 to 2.79 eV. The bandgaps calculated
from the CV measurements are somewhat lower (by 0.09–
0.31 eV) than those obtained from the absorption spectra. By
using the oxidation and reduction onset potentials, the HOMO
levels for these polyamides were calculated and found to be
5.36–5.38 eV (relative to the vacuum energy level), whereas
the values for the lowest unoccupied molecular orbital
(LUMO) levels lay between 2.58 and 2.61 eV (Table 4), which
are similar to those reported for the pyrene-containing triaryl-
amines. As expected, the polyamide 4g possesses a higher
HOMO energy (5.07 eV) and a smaller bandgap (2.43 eV)
when compared with the 4a–f series. The relevant data for
polyamide 4g are consistent with those reported previously
for 40a–d. This also suggests that attaching the carbonyl side
of the amide linkage on the para positions of the DPPA phenyl
units in the present polyamides results in a decrease in
HOMO energy and an increase in bandgap.
Spectroelectrochemical and Electrochromic Properties
Spectroelectrochemical measurements were tested on films
of polymers drop-coated onto ITO-coated glass slides
immerged in electrolyte solution. The electrode preparations
and solution condition were identical to those used in the
CV experiments. The UV–vis–NIR absorption spectra of
PYRENYLAMINE-FUNCTIONALIZED AROMATIC POLYAMIDES, KUNG AND HSIAO
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
for purple coloring at electrode potential of 1.45 V. A similar
spectral change was observed for analogous polyamides 4a,
4b, and 4d–f during the oxidation process. For example, the
spectroelectrochemical series of polyamide 4b are included
in the Supporting Information Figure S6. Moreover, color
changes were also observed in these polyamides on reduc-
tion. Figure 8(a) inset illustrates the spectral and coloration
changes of 4c on electro-reduction. However, the color
change (colorless to light yellow) is not strong as that
observed in the anodic scanning.
The electro-optical properties of polyamide 4g were also
deciphered using the changes in electronic absorption spec-
tra on both oxidation and reduction process (Fig. 9). This
polyamide exhibited ambipolar and multicolored electrochro-
mic behaviors arising from the DPPA segments linked to
different sides of the amide linkage. When the applied poten-
tials increased positively from 0 to 1.0 and 1.5 V, corre-
sponding to the first and second electron oxidation, the
characteristic absorption bands at 335 and 369 nm for neu-
tral-form polyamide 4g decreased gradually and batho-
chromically shifted to 549 and 594 nm, accompanied by the
concomitant formation of new broad long-wavelength
absorption bands centered on 834 nm. The spectral changes
are apparently arisen from the sequential oxidation proc-
esses of the amino centers in the two DPPA segments of dif-
ferent electronic nature in the polymer backbone of 4g. As
shown in Figure 9(a) inset, the polymer film showed a dual-
colored electrochromic behavior on electro-oxidation, with a
coloration change from pale yellow (L: 94.5; a: ꢁ6.7; and b:
50.0), through greenish-gray (L: 73.0; a: ꢁ9.0; and b: 23.2),
and to dark purplish-gray (L: 46.0; a: 5.2; and b: ꢁ12.9).
When the applied potentials increased negatively from 0 to
ꢁ2.0 and ꢁ2.4 V, corresponding to the first and second elec-
tron reduction, the characteristic absorption bands at 335
and 368 nm for neutral-form polyamide 4g maintained their
absorptions and accompanied by the concomitant formation
of new sharp long-wavelength absorption bands centered on
503 nm in visible region. The spectral changes are appa-
rently arisen from the sequential reduction processes of the
pyrene units of slightly different electronic nature in the
polymer backbone of 4g. As illustrated in Figure 9(b) inset,
the polymer film of 4g changes from neutral pale yellow,
through bright yellow (L: 85.0; a: 1.1; and b: 64.1) at ꢁ2.0 V,
and to reddish-orange (L: 63.0; a: 52.1; b: 70.6) at ꢁ2.4 V.
The possible oxidation and reduction orders of the redox-
active units of polyamide 4g are proposed in Figure 9(c).
The Epa and Epc values indicated in each amino center and
the pyrene units were taken from the CV or DPV diagram of
4g. Thus, the incorporation of DPPA units into both of the
diacid and diamine components causes the polyamide to ex-
hibit different oxidation states which make it to be a multi-
colored anodically and cathodically coloring material.
FIGURE 6 Cyclic voltammograms of the cast films of polya-
mides (a) 4c and (b) 4g on an ITO-coated glass substrate in 0.1
M TBAClO4 acetonitrile (for the anodic oxidation process) and
DMF (for the cathodic reduction process) solutions at
a
scan rate of 50 and 100 mV/s, respectively. [Color figure can
be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
polyamide 4c film at various applied potentials are shown in
Figure 8, which is representative for the other 4a–4f coun-
terparts. In the neutral form, polyamide 4c exhibited strong
absorptions at 334 and 355 nm, characteristic for p–p* tran-
sitions, but it was almost transparent in the visible and NIR
regions. The optical bandgap of polymer 4c was calculated
as 2.85 eV from the onset of the p–p* transition at 435 nm.
On electro-oxidation of the 4c film (increasing applied volt-
age from 0 to 1.45 V), the absorption of p–p* transition at
355 nm gradually decreased, whereas new peaks at 545 and
586 nm gradually increased in intensity. We attribute this
spectral change to the formation of a monocation radical
from the pyrenylamine moiety. The observed electronic
absorption changes in the film of 4c at various potentials are
associated with strong color changes; indeed, they even can
be seen readily by the naked eye. From the photos shown in
Figure 8(b) inset, it can be seen that the film changed from
a nearly colorless transparent neutral state (L: 94.0; a: ꢁ4.0;
and b: 18.0) to purple oxidized state (L: 65.5; a: 15.0; and b:
ꢁ13.9). Dynamic changes in % transmittance of 355, 545,
and 586 nm at varying applied potentials are illustrated in
Figure 8(b). The electrochromic polymer 4c shows a relative
high optical contrast in visible region with a transmittance
change (%DT) of 44.7% at 545 nm and 46.8% at 586 nm
Electrochromic Stability
Electrochromic switching studies for the polyamides were
performed to monitor the percent transmittance changes
(D%T) as a function of time at their absorption maximum
and to determine the response time by stepping potential
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ARTICLE
FIGURE 7 (a) DPV of the cast film of polyamide 4g on the ITO-coated glass substrate in 0.1 M TBAClO4/DMF solution for cathodic
reduction process. Scan rate, 10 mV/s; pulse amplitude, 50 mV; pulse width, 50 ms; and pulse period, 0.2 s. (b) Cyclic voltammo-
grams of 10 mM of diamide model compounds M1 and M2 in DMF containing 0.1 M TBAClO4 at a Pt coil electrode, scan rate ¼
100 mV. (c) Cyclic voltammograms of polyamide 4g films at various potential scan rates for the first anodic oxidation process.
(d) Plots of the current densities versus the scan rates for polyamide 4g films. [Color figure can be viewed in the online issue,
which is available at wileyonlinelibrary.com.]
FIGURE 8 (a) Spectroelectrochemistry of the aramid 4c thin film on the ITO-coated glass substrate in 0.1 M TBAClO4/CH3CN at var-
ious applied potentials. (b) Optical change in T% as a function of applied potential for the three absorption bands at 355, 545, and
586 nm. The photographs show the color change of the film on an ITO electrode at indicated potentials. [Color figure can be
viewed in the online issue, which is available at wileyonlinelibrary.com.]
PYRENYLAMINE-FUNCTIONALIZED AROMATIC POLYAMIDES, KUNG AND HSIAO
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 10 Dynamic changes of (a) absorption, (b) current den-
sities, and (c) optical transmittance monitored for polyamide
4g at 834 nm, stepped between 0.0 and 1.00 V (vs. Ag/AgCl).
The red solid-dot shows (d) the variation in the CE after differ-
ent switching cycles. [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com.]
FIGURE 9 Spectral changes of the cast film of polyamide 4g on
the ITO-coated glass substrate on (a) p-doping 0.1 M TBAClO4/
CH3CN and (b) n-doping in 0.1 M TBAClO4/DMF at various
applied potentials (vs. Ag/AgCl). (c) The possible redox order
for the DPPA segments in the repeating unit of polyamide 4g.
[Color figure can be viewed in the online issue, which is avail-
able at wileyonlinelibrary.com.]
repeatedly between the neutral and oxidized states. The
active area of the polymer film on ITO-glass is ꢃ1 cm2. As a
typical example, Figure 10 depicts the optical transmittance
and current density changes of polyamide 4g as a function
of time at their longer wavelength absorption maxima (597
and 834 nm) by applying squarewave potential steps of 11 s
FIGURE 11 (a) Photos of sandwich-type ITO-coated glass single
layer electrochromic device, using polyamide 4g as active
layer. (b) Schematic illustration of the structure of the electro-
chromic device. [Color figure can be viewed in the online issue,
which is available at wileyonlinelibrary.com.]
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WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
(complete cycle time is 22 s) between 0 and 1.0 V. The
response time was calculated at 90% of the full-transmit-
tance change because it is difficult to perceive any further
color change with naked eye beyond this point. Polyamide
4g attained 90% of a complete coloring and bleaching switch
in less than 4 s (3.8 s for coloring) and 2 s (1.6 s for bleach-
ing), respectively. As shown in Figure 10(a,b), the absorbance
changes at 834 nm reflect the switch in current, and the
kinetics of the charge transport process can be referenced to
the coloration response time. Coloration efficiency (CE; g) is
a useful term for measuring the power efficiency of the elec-
trochromic devices and can be calculated via optical density
using the following equation:28
in the deep blue region together with an enhanced fluores-
cence quantum efficiency. Reported properties prove that the
polyamides are multifunctional materials which may find
optoelectronic applications in OLEDs and electrochromic
devices.
The authors thank the National Science Council of Taiwan, ROC,
for the financial support of this work (Grant No. NSC 97-2221-
E-027-112-MY3).
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