New conducting polymers based on poly(3,4-ethylenedioxypyrrole): Synthesis, characterization, and properties

Article abstract of DOI:10.1246/cl.2004.46

Solution-processible conducting polymers 1 and 2, based on 3,4-ethylenedioxypyrrole, were synthesized. A comparison of the polymers' optical and electrical properties showed that the introduction of a vinyl group in polymer 1 produced a decrease of bandga

Full text of DOI:10.1246/cl.2004.46

46
Chemistry Letters Vol.33, No.1 (2004)
New Conducting Polymers Based on Poly(3,4-ethylenedioxypyrrole):
Synthesis, Characterization, and Properties
In Tae Kim,Ã Jung Youl Lee, and Sang Woo Lee
Department of Chemistry, Kwangwoon University, 447-1 Wolgye-Dong, Nowon-Ku, Seoul 139-701, Korea
(Received September 16, 2003; CL-030870)
Solution-processible conducting polymers 1 and 2, based on
O
O
O
O
3,4-ethylenedioxypyrrole, were synthesized. A comparison of
the polymers’ optical and electrical properties showed that the
introduction of a vinyl group in polymer 1 produced a decrease
of bandgap. This occurrence was attributed to the enhancement
of the planarity of polymer 1.
H3CO
HO
OCH3
OH
c
N
N
O
O
(CH2)11
CH3
3
(CH2)11
CH3
5
d
a
Electronically conducting polymers are known to be excel-
lent materials for electronic devices like electrolytic capacitors,
actuators, sensors, artificial muscles, and light-emitting diodes
(LEDs).1 Electron-rich conducting polymers, such as polypyr-
role (PPY), poly(3,4-ethylenedioxythiophene) (PEDOT), poly-
( p-phenylenevinylene) (PPV), poly(3,4-ethylenedioxypyrrole)
(PEDOP), and N-substituted poly(3,4-propylenedioxypyrrole)
(ProDOP), are useful for the formation of stable conjugated pol-
ymer complexes that can be rapidly switched between their oxi-
dized and neutral states.2 In the case of PEDOT and PEDOP,
ethylenedioxy substitution served to enhance their optical, elec-
trochemical, and electronic properties.3 The bandgap of PPV is
lower by 0.3 eV than that of its parent, polyphenylene. The vi-
nylene linkage not only reduces the bandgap of the PPV but also
acts as conjugated spacer to increase the degree of coplanarity of
the PPV backbones.4 A soluble processible electron-rich low
bandgap (1.67 eV) conducting poly(1-dodecyl-2,5-pyrrolylene-
vinylenes) (PDPV), prepared through a new synthetic route us-
ing a monomer having a thiophenyl group as the leaving group,
was recently reported.2b
This present study reports the preparation route and the
properties of the electron-rich conjugated polypyrrole deriva-
tives: poly(1-dodecyl-3,4-ethylenedioxy-2,5-pyrrolylene) (1)
and poly(1-dodecyl-3,4-ethylenedioxy-2,5-pyrrolylene vinyl-
ene) (2) as shown in Scheme 2. Dimethyl 1-dodecyl-3,4-ethyl-
enedioxypyrrole-2,5-dicarboxylate (3) was synthesized through
dodecylation on the nitrogen of dimethyl-3,4-ethylenedioxypyr-
role-2,5-dicarboxylate.5 Compound 3 was hydrolyzed in NaOH
aqueous solution to give 1-dodecyl-3,4-ethylenedioxypyrrole-
2,5-dicarboxylic acid. Decarboxylation of 1-dodecyl-3,4-ethyl-
enedioxypyrrole-2,5-dicarboxylic acid in triethanolamine at
180 ꢀC yielded compound 4 as monomer. Monomer 4 was then
smoothly polymerized with iron(III) chloride hexahydrate,
O
O
O
O
PhS
SPh
N
N
(CH2)11
CH3
(CH2)11
CH3
6
4
b
e
O
O
O
O
N
N
n
n
(CH2)11
CH3
(CH2)11
CH3
1
2
Scheme 2. a) i) NaOH, H2O, 100 ꢀC, 24 h, 85%, ii) triethanol-
amine, 180 ꢀC, 15 min, 54%; b) Iron(III) chloride hexahydrate,
acetonitrile, 0 ꢀC, 12 h, hydrazine monohydrate, 82% c) LAH,
THF, 0 ꢀC, 5 h, 63%, d) benzenethiol, ZnI2, CH2Cl2, 18 h,
32%, e) TFA, THF, À28 ꢀC–rt, 24 h, 52%.
yielding polymer 1. The resulting oxidized polymer was washed
with ethanol and reduced in concentrated hydrazine monohy-
drate. It was then reprecipitated in ethanol, producing a black
powder completely soluble in THF, CHCI3, and CH2CI2.6
The reduction of compound 3 with LiAlH4 generated 1-do-
decyl-3,4-ethylenedioxy-2,5-dimethanol (5). Compound 5 was
treated with benzenethiol and ZnI2 in CH2CI2 at room tempera-
ture for 18 h. This process yielded 32% 1-dodecyl-3,4-ethylene-
dioxy-2,5-bis(phenylthiomethylene)pyrrole (6) as monomer.7
Monomer 6 was then polymerized through treatment with tri-
fluoroacetic acid in THF for 24 h, giving poly(1-dodecyl-3,4-eth-
ylenedioxy-2,5-pyrrolylenevinylene) (2). Conversion from mon-
omer 6 gave polymer 2 in 52% yield, which was considerably
higher
than
what
was
typically
obtained
for
poly(phenylenevinylene) prepared from bis(sulfonium) salt pre-
cursors.8 Table 1 gives some properties of polymers 1 and 2. The
resulting deep blue-black conjugated polymer 2 was soluble in a
variety of organic solvents.9
Gel permeation chromatography (GPC) analysis, using
polystyrene standards, gave a number average molecular weight
(Mn) of 5:3 Â 103 for polymer 1 and 1:3 Â 104 for polymer 2.
Thermogravimetric analysis (TGA; N2; 10 ꢀC/min) of polymer
1 showed the onset of decomposition at 275 ꢀC and 15% weight
loss by 475 ꢀC. On the other hand, polymer 2 showed the onset of
N
(CH2)11
CH3
n
PDPV
Scheme 1.
Copyright Ó 2004 The Chemical Society of Japan

Chemistry Letters Vol.33, No.1 (2004)
47
Table 1. Properties of the polymer 1 and 2
interactions of adjacent pyrrole rings in polymer 1, therefore in-
creasing the degree of coplanarity of the conjugated polymer 2
backbones.
In summary, a new low bandgap electron-rich polymer 2
was prepared. This polymer was dark blue-black in the neutral
state and became transparent light yellow-greenish when doped.
According to the results obtained for polymer 2, it was clear that
the principle of inducing smaller bandgap into conducting poly-
mers by a regular alternating of vinyl group and pyrrole ring
moieties worked well.
ꢁ max/nm
Mw Conductivity Bandgap
S cmÀ1
(dopant)
Polymer
Mn
CHCl3
Mn
/(eV)
2:8 Â 10À2
Polymer 1
Polymer 2
312
659
5310 4.51
13000 1.53
3.26
1.57
(I2)
0.45
(I2)
decomposition at 170 ꢀC and 15% weight loss by 240 ꢀC. Thus,
polymer 1 appeared to be more thermally stable than polymer 2.
The electrical conductivity of polymers 1 and 2 were meas-
ured using a standard four-probe technique. The polymer 1 and 2
showed insulator properties without dopants. Table 1 shows the
maximum conductivity values for polymer 1 and polymer 2
films with I2 dopant. Polymer 2, which had higher molecular
weight, gave an electrical conductivity of about 0.45 ScmÀ1 with
I2 as dopant. Polymer 1, on the other hand, had an electrical con-
ductivity of 2:8 Â 10À2 ScmÀ1. The discrepancy in the electrical
conductivity of polymers 1 and 2 suggested that the low conduc-
tivity of polymer 1 arises from significant steric interactions be-
tween the 1-dodecyl-3,4-ethylenedioxy pyrrole rings. These
conductivity values suggested that polymer 2, with long effec-
tive conjugation lengths, would exhibit comparable electrical
conductivity of PDPV. On long term (1 month) exposure to
air, undoped (neutral state) polymer 2 apparently became oxy-
gen doped, showing a maximum conductivity of 1:53 Â
This work was supported by research grants from the RRC
program of MOST and KOSEF and Kwangwoon University
(2002).
References and Notes
1
2
T. A. Skotheim, R. L. Elsenbumer, and J. R. Reynolds,
‘‘Handbook of Conducting Polymers,’’ 2nd ed., Dekker,
New York (1998).
a) C. L. Gaupp, K. Zong, P. Schottland, S. C. Thompson, C.
A. Thomas, and J. R. Reynolds, Macromolecules, 33, 1132
(2000). b) I. T. Kim and R. L. Elsenbaumer, Macromole-
cules, 33, 6407 (2000). c) Y. Fu, H. Cheng, and R. L.
Elsenbaumer, Chem. Mater., 9, 1720 (1997). d) G. Sonmez,
¨
I. Schwendeman, P. Schottland, K. Zong, and J. R. Reynolds,
Macromolecules, 36, 639 (2003).
3
4
H. Eckhardt, L. W. Shacklette, K. Y. Jen, and R. L.
Elsenbaumer, J. Chem. Phys., 91, 1303 (1989).
a) G. A. Sotzing and K. Lee, Macromolecules, 35, 7281
(2002). b) K. Shiraishi and T. Yammamoto, Synth. Met.,
130, 139 (2002).
10À7 ScmÀ1
.
The UV–vis absorption maximum was at 312 nm for poly-
mer 1 and 659 nm for polymer 2 in THF solutions (Figure 1).
These UV–vis absorption data suggested that polymer 2 has con-
siderably longer conjugation length than that of polymer 1.
Bandgap (band edge) of 1.57 eV was obtained for polymer 2,
which was lower than that of polymer 1, 3.26 eV. But, the band-
gap of polymer 2 is compareable to that of PDPV (1.67 eV). This
result was attributed to the vinylene linkage in polymer 2. This
linkage not only extended the electronic properties of the poly-
mer chain but also acted as a conjugated spacer to reduce steric
5
6
A. Merz, R. Schropp, and E. Dotterl, Synthesis, 1995, 795.
¨
Polymer 1, IR: 2916, 2855, 1602, 1511, 1456, 1329, 1073,
927, 848 cmÀ1. Eg (Band edge) = 3.26 eV. 1H NMR(in
Acetone-d6), ꢀ 4.26(s, 4H); 3.69(s, 2H); 1.28(m, 20H);
0.88(s, 3H). 13C NMR(in Acetone-d6), ꢀ 131.97; 129.64;
66.53; 66.22; 32.76; 30.27; 30.12; 29.97; 29.81; 29.66;
29.51; 27.51; 24.16; 19.98; 14.37. Anal. Calcd for
C18H31NO2: C, 74.18; H, 10.03; N, 4.81; O, 10.98%. Found:
C, 74.63; H, 9.96; N, 4.91; O, 10.40%.
7
8
9
H. Chang and R. L. Elsenbaumer, J. Chem. Soc., Chem.
Commun., 1995, 1451.
R. W. Lenz, C. C. Han, J. S. Stenger, and F. E. Kaeasz, J.
Polym. Sci., Part A: Polym. Chem., 26, 3211 (1988).
Polymer 2, IR: 3068, 2922, 2849, 1694, 1535, 1402, 1262,
1110, 1049, 970 cmÀ1. Eg (Band edge) = 1.57 eV. 1H
NMR(in CD2Cl2), ꢀ 6.95(s, 1H); 4.43(s, 4H); 3.84(s, 2H);
2.45(s, 2H); 1.67(s, 2H); 1.26(m, 20H); 0.87(s, 3H). 13C
NMR(in CDCl3), ꢀ 152.22; 144.33; 136.40; 128.85;
125.95; 67.27; 66.69; 34.93; 34.66; 32.49; 30.64; 30.24;
29.93; 28.72; 28.48; 27.32; 23.25; 21.37. Anal. Calcd for
C40H66N2O4: C, 75.43; H, 10.43; N, 4.00; O, 10.04%.
Found: C, 75.30; H, 9.37; N, 4.00; O, 10.80%.
Figure 1. UV–vis spectra of polymer 1 and 2 in THF.
Published on the web (Advance View) December 15, 2003; DOI 10.1246/cl.2004.46