2
J. Bae et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
0
methods such as ultraviolet–visible (UV–Vis), Fourier transform
infrared (FTIR), Raman and photoluminescence (PL) spectroscopy
have been used to assess the electrochemistry of TPA derivatives
and identify the species formed during the electrochemical process
2.1.2. Synthesis of 4,4 -dinitrotriphenylamine
Aniline (2.15 g, 23.1 mmol), 4-fluoronitrobenzene (7.24 g,
51.3 mmol) and cesium fluoride (7.79 g, 51.3 mmol) were dis-
solved in dried 100 ml DMSO, and the reactant mixture was stirred
at 120 °C for 48 h. The reaction mixture was cooled to room tem-
perature, poured into 500 ml of cold water and the precipitated or-
ange solid was then collected by filtration and washed with
methanol. The product yield was 5.58 g (68%); H NMR (DMSO-
6
d , ppm): 7.18–7.22 (m, Ar–H, 4H), 7.26–7.29 (d, Ar–H, 2H),
7.33–7.41 (t, Ar–H, 1H), 7.48–7.56 (t, Ar–H, 2H), 8.16–8.23 (m,
Ar–H, 4H).
[
8–10]. On the other hand, the electrochemical process of the poly-
mer-containing TPA derivatives is not completely understood.
Moreover, few studies have examined the species formed during
the electrochemical oxidation of TPA-units based on the electro-
chemical process of aniline-containing materials.
1
0
In this study, the polyamide was synthesized using 4,4 -diam-
inetriphenylamine and dicarboxylic acid monomer solution poly-
merization (Fig. 1) [11]. This study examined the electrochemical
process of TPA-based polyamide film using cyclic voltammetry
0
2.1.3. Synthesis of 4,4 -diaminotriphenylamine
0
(
CV) and UV–Vis absorption spectroscopy. In addition, the oxida-
A mixture containing 5.0 g (14.1 mmol) of 4,4 -dinitrotriphenyl-
tive reaction of TPA-based polyamide films was examined by FTIR
spectroscopy. FTIR spectroscopy is a very sensitive technique that
can be used to identify the specific functional groups in polymer
chains and examine the structural changes in electroactive mate-
rials involving the oxidation and protonation process [12]. More-
over, a more detailed investigation of TPA-based polyamide was
performed by closely examining the oxidative reaction of TPA
unit-induced structure changes during the electrochemical pro-
cess using two-dimensional (2D) correlation analysis. As reported
previously [13,14], the 2D gradient mapping method was used to
examine the detailed spectral changes in the UV–Vis absorption
spectra during the electrochemical process of the TPA-based poly-
amide films.
amine, 2.52 g (40.0 mmol) of hydrazine monohydrate, 0.2 g of 10%
Pd–C and 100 ml of ethanol was stirred at 120 °C for 8 h. The reac-
tion mixture was filtered through a Celite pad to remove Pd–C, and
the filtrate was added to 100 ml of water to produce the precipi-
tates, which were then filtered and dried. The crude product was
recrystallized from ethanol. The product yield was 3.56 g (92%);
1
6 2
H NMR (DMSO-d , ppm): 4.97 (s, Ar–NH , 4H), 6.50–6.82 (m,
Ar–H, 7H), 6.78–6.82 (d, Ar–H, 4H), 7.02–7.08 (t, Ar–H, 2H).
2.1.4. Synthesis of polyamide
Polyamide with a triphenylamine moiety in the main chain was
0
synthesized from the direct polycondensation of 4,4 -diaminotri-
phenylamine and terephthalic acid as follows [11]. A mixture
0
containing terephthalic acid (0.91 g, 5.45 mmol), 4,4 -diaminotri-
phenylamine (1.50 g, 5.45 mmol), 40 ml of NMP/pyridine (v/v = 4/
2
. Experimental
1
), and triphenylphosphine (3.14 g, 12.0 mmol) was stirred at room
temperature under nitrogen for 2 h. The reaction mixture was
heated to 100 °C for an additional 12 h. The reaction solution was
then poured into hot methanol with vigorous stirring, producing
2
2
.1. Materials and synthesis
.1.1. Materials
1
polyamide as the powder precipitate in 92% yield. H NMR
Aniline (TCI), potassium permanganate (Aldrich), 4-fluoroni-
(
DMSO-d
6
, ppm): 6.91–7.15 (m, Ar–H, 7H), 7.21–7.48 (t, Ar–H,
trobenzene (from Alfa Aesar), cesium fluoride (Aldrich), hydrazine
monohydrate (Aldrich), tetrabutylammonium perchlorate (TPBA)
and 10% palladium on activated carbon (Aldrich) were used as re-
ceived. Dimethyl sulfoxide (DMSO), acetonitrile, N,N-dimethyl-
acetamide (DMAc) and pyridine (Py) were purchased from
Aldrich, and used as received. The solvent for polymerization,
N-methyl-2-pyrrolidinone (NMP), was obtained from Aldrich,
purified by distillation over calcium hydride and stored over 4 Å
molecular sieves.
2
1
H), 7.68–7.82 (d, Ar–H, 4H), 8.01–8.22 (s, Ar–H, 4H), 10.31–
0.47 (s, Ar–NH, 2H).
2.2. Measurements
g
The glass transition temperature (T ) and degradation tempera-
d
ture (T ) of polyamide were measured by DSC (model DSC-7, Per-
kin-Elmer, USA) and TGA (model TGA-7, Perkin–Elmer, USA),
respectively. In the DSC and TGA measurements, dry nitrogen gas
was purged at a flow rate of 100 cc/min and a ramping rate of
1
0.0 °C/min was used. The inherent viscosity of polyamide product
in DMAc with a concentration of 0.50 g/dL was measured at 25.0 °C
using an Ubbelohde suspended-level capillary viscometer. A poly-
amide solution was spin-cast onto indium tin oxide (ITO)-coated
glass and gold-coated silicon wafer substrates for the UV–Vis spec-
troscopy and FTIR spectroscopy, respectively, followed by drying in
a vacuum oven at 80 °C for 1 day. The UV–Vis absorption spectra
were obtained as a function of the exposure dose using a Hew-
lett–Packard 8453 spectrophotometer. FTIR spectroscopy was car-
ried out on a Bruker Vertex 80/v FTIR spectrometer equipped with
an ATR accessory (PIKE) at the Pohang Accelerator Laboratory
H N
NH2
2
O
O
N
+
HO
OH
–
1
(
PAL). The FTIR spectra were recorded at a 4 cm resolution with
a liquid-nitrogen-cooled mercury cadmium telluride (MCT) detec-
tor. Cyclic voltammetry (Epsilon) was performed using a three-
electrode cell, in which ITO (with a polymer film area of ca.
O
C
O
C
H
H
N
N
N
2
0
.5 ꢁ 1.1 cm ) was used as the working electrode. The electro-
chemical cell was composed of a 1 cm cuvette, ITO as the working
electrode, platinum wire as the auxiliary electrode, and Ag/AgCl as
the reference electrode. The 2D correlation spectra were obtained
using an algorithm based on a numerical method reported by Noda
[15–17]. 2D correlation analysis was performed after a baseline
Fig. 1. Molecular structure of TPA based polyamide.