Facile fabrication of redox-active and electrochromic poly(amide-amine) films through electrochemical oxidative coupling of arylamino groups

Article abstract of DOI:10.1002/pola.28124

Two novel electropolymerizable monomers, namely 3,5-bis(4-diphenylaminobenzamido)-N-[4-(carbazol-9-yl)phenyl]benzamide (5) and 3,5-bis(4-diphenylaminobenzamido)-N-[4-(3,6-dimethoxycarbazol-9-yl)phenyl]benzamide (5-MeO), were synthesized, and their electro

Full text of DOI:10.1002/pola.28124

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Facile Fabrication of Redox-Active and Electrochromic
Poly(amide-amine) Films Through Electrochemical Oxidative
Coupling of Arylamino Groups
Sheng-Huei Hsiao, Hui-Min Wang
Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, Taipei 10608, Taiwan
Correspondence to: S.-H. Hsiao (E-mail: shhsiao@ntut.edu.tw)
Received 17 February 2016; accepted 17 March 2016; published online 00 Month 2016
DOI: 10.1002/pola.28124
ABSTRACT: Two novel electropolymerizable monomers, namely
,5-bis(4-diphenylaminobenzamido)-N-[4-(carbazol-9-yl)phenyl]-
benzamide (5) and 3,5-bis(4-diphenylaminobenzamido)-N-[4-
3,6-dimethoxycarbazol-9-yl)phenyl]benzamide (5-MeO), were
chromic and fluorescent properties (the emission of blue light
(460 nm) in solid state). Both of the electro-generated polymer
films derived from 5 and 5-MeO showed reversible electro-
chemical oxidation processes in the range of 0 2 1.4 V with
strong color changes and high contrast ratios in the visible and
3
(
synthesized, and their electrochemical properties were studied
by cyclic voltammetry. The electron-withdrawing amide groups
efficiently blocked the radical cations delocalization between
the two terminal TPA groups, rendering the electropolymeriza-
tion of the TPA groups feasible. The polymer electrodeposited
from monomer 5 could be further crosslinked through electro-
coupling of the carbazole groups, which showed both electro-
NIR regions upon electro-oxidation. C
V
2016 Wiley Periodicals,
Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 00, 000–000
KEYWORDS: carbazole; electrochemistry; fluorescence; poly(am-
ide-amine)s; redox polymers; triphenylamine
INTRODUCTION Electrochromism involves the process of
ductors and hole-transporting materials for various electro-
1
1
changing the absorption profile of a material with applica-
optical applications.
Due to the good electron-donating
1
tion of an electric field or passing of electrical charge. This
nature of triarylamines, their derived oligomers and poly-
mers have been widely studied as hole-transporting materi-
als for a number of applications, such as xerography, organic
field-effect transistors, photovoltaics, organic light-emitting
interesting property led to the development of many techno-
2
logical applications such as smart windows, color changing
3
4
5
eyewear, display devices, and military camouflage. Recent
high-profile commercialization of electrochromic materials
includes the Boeing 787 Dreamliner windows manufactured
9
–11
devices, and so forth.
In addition, the application of
redox-active polymers as active electrode materials has
attracted much attention in the area of secondary battery
6
by Gentex. Up to now, many organic and inorganic materials
1
2
have been developed for electrochromic applications, such as
inorganic metal oxide, mixed-valence metal complexes,
research during the past few decades. For example, redox-
1
3
14
active polytriphenylamine
and poly(N-vinylcarbazole)
7
organic small molecules, and conjugated polymers. Among
have been evaluated as cathode active materials for use in
rechargeable lithium batteries.
the many different kinds of electrochromic materials avail-
able, electrochromic conjugated polymers have received tre-
mendous attention due to their fine-tuning of coloration,
high coloration efficiency, fast switching speeds, high con-
Molecules containing electroactive carbazole and triphenyl-
amine (TPA) moieties are interesting materials because their
redox and photophysical properties make them suitable for
8
trast ability, and good processability.
1
0
use as hole carriers in optoelectronic devices. In the past
decade, a huge amount of high-performance polymers (typi-
cally, aromatic polyamides and polyimides) carrying the TPA
and/or carbazole unit have been prepared and evaluated for
Arylamine-based derivatives have attracted significant atten-
tion in the past years due to their unique properties that
allow them to have potential applications in organic elec-
9
15
tronics, photonics and magnetic materials. Most of the hole-
electrochromic applications. It is well known that the one-
transporting materials contain triarylamine moieties in their
molecular structures. Many star-shaped, dendrimeric and
polymeric triarylamines have been synthesized as photocon-
electron oxidation of unsubstituted TPA causes the genera-
tion of reactive radical cations, which typically undergo irre-
versible dimerization to tetraphenylbenzidine (TPB) as a
1
0
V
2016 The Authors. Journal of Polymer Science Part A: Polymer Chemistry Published by Wiley Periodicals, Inc.
C
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reproduction in any medium, provided the original work is properly cited.
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SCHEME 1 Synthetic route to star-shaped monomers 5 and 5-MeO.
1
6
result of oxidative coupling. The dimerization occurs exclu-
sively in the para position to the nitrogen centers, that is, the
sites with the highest spin electron density. In general, the
TPA dimerization reaction does not extend into a polymeriza-
tion process because of the relatively higher stability of TPB
an 1,3,5-trisubstituted benzene ring as an interior core
bridged by amide linkages terminal electroactive TPA and car-
bazole units. In addition to the polymer formed through TPA
dimerization of monomer 5, the presence of the carbazole
moiety would lead to further electrochemical crosslinking pro-
cess. For a comparative study, an analogous star-shaped mole-
cule 5-MeO with methoxy groups substituted on the active C-
3 and C-6 sites of the carbazole unit was also synthesized,
and its electrochemical behavior was investigated. Both of the
electro-generated poly(amide-amine) films from monomers 5
and 5-MeO displayed fluorescent and electrochromic proper-
ties. This work provides a model to design star-shaped mono-
mers capable to form electrochemically active polymers with
potential applications in electronic and optoelectronic devices.
17
radical cation. The introduction of a nonconjugated spacer or
an electron-deficient group, such as amide, imide, or oxadia-
zole units between the two TPA groups, however, increases
the dimerization reactivity of the TPA radical cation, allowing
individual TPA to realize an independent coupling reaction and
rendering the electropolymerization process feasible. Simi-
larly, as reported by Ambrose and coworkers in their pioneer-
ing work devoted to anodic oxidation of carbazole and
1
8
19
various N-substituted carbazoles, ring–ring coupling is the pre-
dominant decay pathway, the carbazole radical cation yielding
0
3
,3 -bicarbazyls. Although these bicarbazyls possess a lower
EXPERIMENTAL
first oxidation potential than the corresponding monomers
and are therefore, potentially, more suitable for electrochemical
polymerization, dimers were cleanly obtained in quantitative
yields, because of the high stability of the oxidized states
Materials
As shown in Scheme 1, the diamino compounds N-(4-(carba-
zol-9-yl)phenyl)-3,5-diaminobenzamide (4) (mp 5 237–238
8C) and N-[4-(3,6-dimethoxycarbazol-9-yl)phenyl]-3,5-diamino-
benzamide (4-MeO) (mp 5 238–239 8C) were synthesized
according to a literature method. The synthetic details and
their characterization data have been reported in our previous
publications. 4-Carboxytriphenylamine was synthesized by
the cesium fluoride (CsF)-mediated N-arylation reaction of
diphenylamine with p-fluorobenzonitrile, followed by the alka-
20
(bicarbazylium cations). Polymerization may occur anodically
by using bis(carbazole)s, N-linked by a spacer, to produce
2
2
2
1
materials with redox properties characteristic to bicarbazyls.
2
3
Electrochemical polymerization provides the unique advantage
to combine both synthesis and direct fabrication of electroac-
tive polymer films on the electrode surface. This procedure
significantly shortens the experimental time and avoids the
solubility issues often encountered with conventional chemical
methods, thus enlarging the scope of candidate polymers for
electrochromic applications. As a continuation of our recent
efforts in developing elecrochromic materials by electrochemi-
cal synthesis, herein we design and synthesize a novel electro-
polymerizable star-shaped monomer 5 (Scheme 1) featuring
2
4
line hydrolysis of the intermediate 4-cyanotriphenylamine.
N-(4-Aminophenyl)carbazole was prepared by the fluoro-
displacement of p-fluoronitrobenzene with carbazole in the
presence of CsF in dimethyl sulfoxide (DMSO), followed by
Pd/C-catalyzed hydrazine reduction of the intermediate N-(4-
2
4
nitrophenyl)carbazole.
Tetrabutylammonium perchlorate
(Bu NClO , TCI) was recrystallized twice from ethyl acetate
4
4
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FIGURE 1 IR spectra of the synthesized compounds. [Color figure can be viewed in the online issue, which is available at wileyon-
linelibrary.com.]
and then dried in vacuo before use. All other solvents and
hot water, and dried to give 0.65 g of the desired monomer
reagents were used as received from commercial sources.
5 as white powder in 99% yield.
2
1
21
IR (KBr): 3300 cm (amide N 2 H stretching); 1640 cm
1
Synthesis of Star-Shaped Monomers 5 and 5-MeO
(amide C 5 O stretching). H NMR (500 MHz, CDCl
, d, ppm):
3
N-(4-(Carbazol-9-Yl)Phenyl) [3,5-Bis
6.94 (d, J 5 8.5 Hz, 4H, H ), 7.09 (m, 12H, H 1 H ), 7.26 (m,
j
m
k
(4-Diphenylaminobenzamido)]Benzamide (5)
12H, H 1 H 1 H ), 7.35 (t, J 5 9.0 Hz, 2H, H ), 7.45 (d,
b d l c
In a 50-mL round-bottom flask equipped with a stirring bar,
J 5 8.5 Hz, 2H, H ), 7.68 (d, J 5 8.5 Hz, 4H, H ), 7.96 (two
e
i
a mixture of 0.275 g (0.7 mmol) of diamino compound 4,
overlapped doublets, 4H, H
f
1 H
), 8.13 (d, J 5 7.5 Hz, 2H,
g
0
.424 g (1.5 mmol) of 4-carboxytriphenylamine, 0.7 mL of
H
a
), 8.27 (s, 1H, H
amide H ). Anal. Calcd. for C63H N O
46 6 3
h
), 8.59 (s, 2H, amide H
), 9.37 (s, 1H,
o
triphenyl phosphite (TPP), 0.25 mL of pyridine, and 1 mL of
NMP was heated with stirring at 120 8C for 3 h. The solution
was poured slowly with stirring into 150 mL of methanol to
precipitate white product. The precipitated product was col-
lected by filtration, washed repeatedly with methanol and
n
(935.09): C, 80.92%;
H, 4.96%; N, 8.99%. Found: C, 80.55%; H, 4.93%; N, 8.90%.
N-(4-(3,6-Dimethoxycarbazol-9-Yl)Phenyl) [3,5-Bis
(4-Diphenylaminobenzamido)]Benzamide (5-MeO)
In a 50-mL round-bottom flask equipped with a stirring bar,
a mixture of 0.317 g (0.7 mmol) of diamino compound 4-
MeO, 0.434
g (1.5 mmol) of 4-carboxytriphenylamine,
0.70 mL of triphenyl phosphite (TPP), 0.25 mL of pyridine,
and 1 mL of NMP was heated with stirring at 120 8C for 3 h.
The solution was poured slowly with stirring into 150 mL of
methanol to precipitate white product. The precipitated
product was collected by filtration, washed repeatedly with
methanol and hot water, and dried to give 0.64 g of the
desired monomer 5-MeO as white powder in 92% yield.
2
1
21
IR (KBr): 3330 cm (amide N 2 H stretching); 1640 cm
(
1
amide C 5 O stretching). H NMR (500 MHz, CDCl , d,
3
ppm): 3.92 (s, 6H, methoxy H ), 6.91 (d, J 5 8.5 Hz, 4H, H ),
b
j
6.98 (d, J 5 8.5 Hz, 2H, H
c
), 7.07 (m, 12H, H
m
1 H
k
), 7.24
Structure 1. [Color figure can be viewed in the online issue,
(m, 10H, H 1 H ), 7.38 (d, J 5 8.5 Hz, 2H, H ), 7.53 (s, 2H,
d l e
which is available at wileyonlinelibrary.com.]
H ), 7.65 (d, J 5 9.0 Hz, 4H, H ), 7.86 (d, J 5 8.5 Hz, 2H, H ),
g i f
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electrode. All cell potentials were taken with the use of an
Ag/AgCl reference electrode. Ferrocene was used as an
external reference for calibration (10.48 V vs. Ag/AgCl).
Spectroelectrochemical experiments were carried out in a
cell built from a commercial UV–vis cuvette using an Agilent
8453 UV–vis diode array spectrophotometer. The cell was
composed of a 1-cm cuvette, ITO as a working electrode, a
platinum wire as an auxiliary electrode, and an Ag/AgCl ref-
erence electrode.
RESULTS AND DISCUSSION
Monomer Synthesis
The TPA and carbazole-capped star-shaped monomers, 5 and
Structure 2. [Color figure can be viewed in the online issue,
5
-MeO, were prepared by the synthetic route outlined in
Scheme 1. In the first step, the intermediate compounds, N-
4-aminophenyl)carbazole (2) and 3,6-dimethoxy-9-(4-ami-
which is available at wileyonlinelibrary.com.]
(
nophenyl)carbazole (2-MeO) were prepared by the CsF-
mediated nucleophilic displacement reaction of carbazole
7
9
.88 (s, 1H, H
.32 (s, 1H, amide Hn). Anal. Calcd for C H N O
50 6 5
a h o
), 8.24 (s, 1H, H ), 8.61 (s, 2H, amide H ),
65
(995.15): C, 78.45%; H, 5.06%; N, 8.44%. Found: C,
78.25%; H, 4.95%; N, 8.32%.
Preparation of Polymer Films
The electrochemical polymerization experiments were car-
ried out with a CH Instruments 750A electrochemical ana-
lyzer. The polymers were synthesized from the acetonitrile
2
4
solution containing 1.0 3 10
M monomers 5 or 5-MeO
and 0.1 M Bu NClO via cyclic voltammetry repetitive cycling
4
4
at the scan rate of 50 mV/s for ten cycles. The polymer was
deposited onto the surface of the working electrode (ITO/
2
glass surface, polymer films area about 0.8 3 1.25 cm ), and
the film was rinsed with plenty of acetone for the removal of
inorganic salts and other organic impurities formed during
the process.
Instrumentations
Infrared (IR) spectra were recorded on a Horiba FT-720
1
FTIR spectrometer. H NMR spectra were measured on a
Bruker Avance 500 FT NMR system with tetramethylsilane
as an internal standard. Elemental analyses were run in a
Heraeus Vario EL III CHNS elemental analyzer. Ultraviolet-
visible (UV–vis) spectra of the polymer films were recorded
on an Agilent 8453 UV-Visible spectrometer. The absorption
spectra of monomer and polymers were recorded in CH Cl2
2
solution or as solid films on ITO/glass substrate. The optical
bandgaps (E ) of the monomers and polymers were calcu-
g
lated from their absorption edges. Photoluminescence (PL)
spectra were measured with a Varian Cary Eclipse fluores-
cence spectrophotometer. Fluorescence quantum yields (U )
F
of the samples in different solvent were measured by using
quinine sulfate in 1 N H SO as a reference standard
2
4
(
U 5 54.6%). All corrected fluorescence excitation spectra
F
were found to be equivalent to their respective absorption
spectra. Electrochemistry was performed with a CHI 750A
electrochemical analyzer. Cyclic voltammetry was conducted
with the use of a three-electrode cell in which ITO (polymer
1
FIGURE 2 H NMR spectra of monomers (a) 5 and (b) 5-MeO
2
films area about 0.8 3 1.25 cm ) was used as a working
in CDCl . [Color figure can be viewed in the online issue, which
3
electrode. A platinum wire was used as an auxiliary
is available at wileyonlinelibrary.com.]
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FIGURE 3 Cyclic voltammograms and repeated potential scanning of 5 and 5-MeO with a scan rate of 50 mV/s in 0.1 M Bu
CH CN solution. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
4 4
NClO /
3
and 3,6-dimethoxycarbazole, respectively, with p-fluoronitro-
benzene, followed by hydrazine Pd/C-catalytic reduction. The
intermediate dinitro compounds, N-(4-(9H-carbazol-9-
yl)phenyl)-3,5-dinitrobenzamide (3) and N-[4-(3,6-dimethox-
ycarbazol-9-yl)phenyl]-3,5-dinitrobenzamide (3-MeO) were
prepared by condensation of 2 and 2-MeO, respectively, with
gave N-(4-(carbazol-9-yl)phenyl)-3,5-diaminobenzamide (4)
and N-[4-(3,6-dimethoxycarbazol-9-yl)phenyl]-3,5-diamino-
benzamide (4-MeO), respectively. The synthetic details and
the characterization data of diamino compounds 4 and 4-
2
3
MeO were reported previously.
The target star-shaped
monomers 5 and 5-MeO were synthesized from 4 and 4-
MeO, respectively, with 4-carboxytriphenylamine using tri-
phenyl phosphite (TPP) and pyridine as condensing agents.
3,5-dinitrobenzoyl chloride. Reduction of the nitro group of
compound 3 and 3-MeO by means of hydrazine and Pd/C
2
5
FIGURE 4 UV–vis absorption and PL spectra of the dilute solutions of 5 and 5-MeO in CH
2
Cl
2
(1 3 10
M) and the thin film of
Poly-5. Photos show the PL images of the solutions of monomers and the Poly-5 film upon UV exposure (excited at 365 nm).
Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
[
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TABLE 1 Optical Properties of Monomers and Polymers
25
Monomer
CH Cl
2 2
(1 3 10 M) Solution
abs
max
PL
max (nm)
a
CIE 1931
k
(nm)
k
UPL (%)
X
Y
5
5
293, 347
312, 347
460
460
42.6
25.2
0.171
0.171
0.198
0.203
-MeO
Polymer
Film (ꢀ10 lm)
abs
PL
abs
onset
k
max
(nm)
k
max (nm)
k
(nm)
CIE 1931
X
Y
Poly-5
312, 359
312, 361
460
413
420
0.233
–
0.311
–
b
Poly-5-MeO
–
a
b
The fluorescent quantum yield was calculated in an integrating sphere
Difficult to define.
with quinine sulfate as the standard (UPL 5 54.6%).
1
13
IR, H NMR, and C NMR spectroscopic techniques were
used to identify structures of the intermediate compounds
and the target monomers.
patterns were found to grow in intensity on the electrode.
The increase of redox current densities by successive CV
scans indicates the formation of the electrochemically active
polymeric film on the electrode surface. After being
immersed in water for a certain period, a polymer film could
be removed from the ITO-glass surface. The electrodeposited
film of monomer 5 (coded with Poly-5) is proposed to pos-
sess a crosslinked polymer structure formed by the possible
TPA–TPA, carbazole–carbazole, and TPA–carbazole coupling
reactions. As shown in Figure 3(c), monomer 5-MeO shows
two distinguishable oxidation waves in the first CV scan. The
first oxidation wave at Epa 5 1.00 V appears to involve one
electron loss from the 3,6-dimethoxycarbazole unit, and the
second oxidation wave at Epa 5 1.13 V is related to the elec-
tron losses from the TPA unit. The decrease in oxidation
potential of the carbazole unit is apparently attributable to
the introduction of electron-donating methoxy groups on its
C-3 and C-6 positions. As the CV scan continued [Fig. 3(d)],
the increase in the redox wave current densities implied that
the amount of electroactive polymer deposited on the elec-
trode was increasing. The structure of the polymer (Poly-5-
MeO) electropolymerized from monomer 5-MeO is sug-
gested to be linear in large part because the electroactive
sites of the carbazole unit are blocked with methoxy groups
Figure 1 illustrates FTIR spectra of the synthesized com-
pounds 3–5 and 3-MeO to 5-MeO. The IR spectra of com-
pounds 3 and 3-MeO gave characteristic bands of nitro
groups at around 1547 and 1340 cm (2NO2 asymmetric
and symmetric stretching), which disappeared after reduc-
2
1
tion. Diamines 4 and 4-MeO showed a typical 2NH stretch-
2
2
1
ing absorption pair in the region of 3200–3500 cm . After
condensation with 4-carboxytriphenylamine, the characteris-
tic absorptions of the primary amino group disappeared. The
IR spectra of 5 and 5-MeO showed the characteristic amide
absorption bands at around 3300 cm (N-H stretching) and
650 cm (amide carbonyl stretching). Figure 2 illustrates
2
1
2
1
1
the high-resolution proton NMR spectra of 5 and 5-MeO in
CDCl , and the spectra agree well with their proposed molec-
3
ular structures.
Preparation of Polymer Films
All electrochemical polymerization processes of monomers
were performed on the ITO glass slides in a reaction
2
4
medium containing 10
M monomer and 0.1 M Bu NClO4
4
in acetonitrile via repetitive cycling at a potential scan rate
of 50 mV/s. Figure 3(a) displays the first two consecutive CV
scans of 5. For the first positive potential scan, we observe
two overlapped oxidation waves at about 1.14 and 1.35 V,
respectively. It is known that TPA and CBZ moieties can be
oxidized to the respective mono radical cations and that CBZ
is oxidized at a potential higher than that of the structurally
TABLE 2 Optical Properties of Monomers and Polymers
Oxidation
Energy
a
opt
g
b
c
Molecules
Potential (V)
E
(eV)
Levels (eV)
Eonset
E1/2
HOMO LUMO
1
6,19
related TPA.
Thus, we propose that the TPA groups of
5
1.01
0.88
0.75
0.77
1.13, 1.24
1.00, 1.13
1.17
3.10
5.37
5.24
5.11
5.13
2.29
2.15
2.11
2.18
monomer 5 are involved in the first oxidation process and
the CBZ group is involved in the second oxidation process.
In the second scan, a new oxidation peak appeared at a
lower potential of 0.95 V, which might be associated with
the first oxidation process of tetraphenylbenzidine (TPB),
biscarbazole, or the mixed TPA-carbazole structure. As
shown in Figure 3(b), upon repetitive scanning of the solu-
tion of 5 over the voltage range from 0 to 1.4 V, new redox
5
-MeO
3.09
3.00
2.95
Poly-5
Poly-5-MeO
1.20
a
vs. Ag/AgCl in CH
3
CN.
b
Optical bandgap, derived from the optical absorption edge;
opt
g
E
5 1240/konset
.
c
HOMO 5 –(Eonset 1 4.8) (eV); ELUMO 5 EHOMO – E go pt
E
.
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SCHEME 2 Anodic oxidation pathways of (a) TPB and (b) biscarbazole units. [Color figure can be viewed in the online issue, which
is available at wileyonlinelibrary.com.]
and the polymer is mainly built up via the TPA-TPA coupling
reactions.
relevant absorption and PL data are collected in Table 1. The
dilute solutions in CH Cl of monomers 5 and 5-MeO exhib-
2
2
ited two UV-vis absorption peaks at 293–312 and 347 nm,
assignable to the p–p* and n–p* transitions of the carbazole
and TPA moieties. The solutions of monomers 5 and 5-MeO
exhibited blue emission at the maximum peaks of 460 nm
with PL quantum yield of 42.6% and 25.2%, respectively.
The lower UPL of monomer 5-MeO may be attributed to
increased energy dissipation during the excited-state lifetime
Absorption and Fluorescence Properties
All the monomers and polymers were examined by UV–vis
absorption and photoluminescence (PL) spectroscopy. Figure
4
shows the absorption and emission profiles of the mono-
mers and polymers, together with their PL images on expo-
sure to an UV light in both solution and solid states. The
FIGURE 5 Cyclic voltammograms of (a) Poly-5 and (b) Poly-5-MeO polymer films on the ITO-coated glass slide in 0.1 M Bu
4 4
NClO /
CH CN at a scan rate of 50 mV/s. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
3
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FIGURE 6 Scan rate dependence of Poly-5-MeO film on ITO/glass surface in 0.1 M Bu
4
NClO
4
3
/CH CN solution at different scan rates
between 50 and 300 mV/s. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
caused by the conformational changes of the methoxy
groups. Solid film absorption spectra of the polymers were
similar to those in solution, with a slight red-shift of ca. 12–
ited film of Poly-5 displayed a strong blue emission upon
exposure to UV irradiation. The absorption onsets of the
polymer films of Poly-5 and Poly-5-MeO were recorded at
413 and 420 nm, respectively, which correspond to bandg-
aps of 3.00 and 2.95 eV, respectively.
14 nm. As shown in the inset of Figure 4, the electrodepos-
Electrochemical Properties of the Electrodeposited Films
The electrochemical behavior of the electrodeposited poly-
mer films Poly-5 and Poly-5-MeO was investigated by cyclic
voltammetry in a monomer-free Bu NClO /CH CN solution.
4
4
3
The quantitative details are summarized in Table 2. As
shown in Figure 5, both of the Poly-5 and Poly-5-MeO films
showed only one broad oxidation peak, although two oxida-
tion processes of the TBP and biscarbazole moiety were
expected (Scheme 2). The half-wave potentials (E1/2) of
Poly-5 and Poly-5-MeO were read at 1.17 and 1.20 V,
respectively. Figure 6 shows the electrochemical behavior of
the Poly-5-MeO films at different scan rates between 50 and
3
00 mV/s in 0.1 M Bu NClO /CH CN. A linear dependence
4 4 3
of the peak currents as a function of scan rates indicated
that the electrochemical processes are reversible and not dif-
fusion limited, and the electroactive polymer is well adhered
to the working electrode (ITO glass) surface.
The highest occupied molecular orbital (HOMO) and lowest
unoccupied molecular orbital (LUMO) energy levels of the
investigated polymers were estimated from the Eonset values.
Assuming that the HOMO energy level for the ferrocene/fer-
1
rocenium (Fc/Fc ) standard is 4.80 eV with respect to the
zero vacuum level, the HOMO levels for Poly-5 and Poly-5-
MeO were calculated to be 5.11 and 5.13 eV (relative to the
vacuum energy level), respectively. Their LUMO energy levels
deduced from the bandgap calculated from the optical
absorption edge were 2.11 and 2.18 eV, respectively (Table
2). According to the HOMO and LUMO energy levels
obtained, the electro-generated polymer films in this study
might be used as hole injection and transport materials.
FIGURE 7 Spectroelectrochemical measurements and color
changes of (a) Poly-5 and (b) Poly-5-MeO film on an ITO-
coated glass in 0.1 M Bu
4
NClO
4
/CH
3
CN at various applied
Spectroelectrochemical and Electrochromic Properties
Spectroelectrochemistry were performed on the electro-
generated polymeric films on ITO glass to clarify its
potentials (vs. Ag/AgCl). [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
8
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electronic structure and optical behavior upon oxidation.
UV–vis–NIR absorbance curves correlated to applied poten-
tials of the Poly-5 and Poly-5-MeO films are presented in
Figure 7(a,b), respectively. In the neutral state, Poly-5 exhib-
ited strong absorption at wavelength 312 and 359 nm, char-
acteristic for p–p* transition band of the polymer, but it was
almost transparent in the visible region and NIR regions.
Upon oxidation (increasing applied voltage from 0.00 to 1.00
V), the absorption of p–p* transition at 359 nm gradually
decreased while two new absorption peaks at 446 and
ACKNOWLEDGMENT
The authors thank the Ministry of Science and Technology of
Taiwan for the financial support.
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