Synthesis of functionalized thiophenes for the preparation of conducting polymer films with complexing properties

Article abstract of DOI:10.1080/10426500601047503

Four series of novel substituted thiophenes (Schiff bases, esters, amides, and amino acids) have been synthesized and tested for their ability to form conducting polymer films via cyclic voltammetry in order to obtain electrochemical sensors for metal cations. The influence of the nature and size of the substituents on the electropolymerizability of the monomers has been studied. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/10426500601047503

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Synthesis of Functionalized
Thiophenes for the Preparation
of Conducting Polymer Films
with Complexing Properties
A. Brembilla a , A. Collard a , B. Henry a , M.
Jadamiec b , M. Lapkowski b c , M. Matlengiewicz c d
& L. Rodehüser a
a CNRS, Faculté des Sciences et Techniques ,
Université Henri Poincaré Nancy 1 , Vandoeuvre-lès-
Nancy, Cedex, France
b Department of Chemistry , Silesian University of
Technology , Gliwice, Poland
c Polish Academy of Sciences , Institute of Coal
Chemistry , Gliwice, Poland
d Department of Environmental Chemistry and
Technology , Silesian University , Katowice, Poland
Published online: 24 Feb 2007.
To cite this article: A. Brembilla , A. Collard , B. Henry , M. Jadamiec , M.
Lapkowski , M. Matlengiewicz & L. Rodehüser (2007) Synthesis of Functionalized
Thiophenes for the Preparation of Conducting Polymer Films with Complexing
Properties, Phosphorus, Sulfur, and Silicon and the Related Elements, 182:4, 723-734,
DOI: 10.1080/10426500601047503
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Phosphorus, Sulfur, and Silicon, 182:723–734, 2007
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500601047503
Synthesis of Functionalized Thiophenes
for the Preparation of Conducting Polymer Films
with Complexing Properties
A. Brembilla
A. Collard
B. Henry
Universite´ Henri Poincare´ Nancy 1, CNRS, Faculte´ des Sciences et
Techniques, Vandoeuvre-le`s-Nancy Cedex, France
M. Jadamiec
Department of Chemistry, Silesian University of Technology,
Gliwice, Poland
M. Lapkowski
Department of Chemistry, Silesian University of Technology, Gliwice,
Poland and Institute of Coal Chemistry, Polish Academy of Sciences,
Gliwice, Poland
M. Matlengiewicz
Institute of Coal Chemistry, Polish Academy of Sciences, Gliwice, Poland
and Department of Environmental Chemistry and Technology,
Silesian University, Katowice, Poland
¨
L. Rodehuser
Universite´ Henri Poincare´ Nancy 1, CNRS, Faculte´ des Sciences et
Techniques, Vandoeuvre-le`s-Nancy Cedex, France
Four series of novel substituted thiophenes (Schiff bases, esters, amides, and amino
acids) have been synthesized and tested for their ability to form conducting polymer
films via cyclic voltammetry in order to obtain electrochemical sensors for metal
cations. The influence of the nature and size of the substituents on the electropoly-
merizability of the monomers has been studied.
Keywords Conducting polymers, cyclic voltammetry, electropolymerization, substituted
thiophenes
Received January 23, 2006; accepted August 21, 2006.
The authors thank the Centre National de la Recherche Scientifique and the Polish
Academy of Sciences for financial support of this research project via a bilateral exchange
program (no. 14475).
Address correspondence to L. Rodehu¨ser, Laboratoire de Chimie Physique, Organique
et Collo¨ıdale, Universite´ Henri Poincare´ Nancy 1, Unite Mixte CNRS-UHP, BP 239,
Nancy-Vandoeuvre Cedex, 54506 France. E-mail: ludwig.rodehuser@lesoc.uhp-nancy.fr
723

724
A. Brembilla et al.
INTRODUCTION
Conducting polythiophenes
have been used for many different
applications,1 such as light emitting devices,2 capacitors, field-effect
transistors,4 antistatic films,5 or biosensor components.6 The introduc-
tion of different substituents in the thiophene ring allows large varia-
tions of properties of the polymers.7 However, the size of substituents
can significantly influence the process of polymerization and the con-
ductivity of the final polymer chain. Metal coordination to polymer thio-
phenes or mixed thiophene-containing polymers induces equally signif-
icant changes of the properties of the compounds.8
In previous publications, we have shown that silica grafted with com-
plexing groups, such as amino acids or dicarboxylates, are efficient scav-
engers for divalent metal cations9 and can be used for the preparation
of electrochemical detectors.10 To assure electrical conductivity, how-
ever, they were incorporated into a conducting matrix of carbon paste,
which led to sensors of low mechanical stability. If it would be possible
to graft the same type of functional groups on a conducting polymer,
the conducting matrix would no longer be necessary, and the stability
of the device would be largely enhanced.
With the aim of preparing conducting polythiophenes with ion-
complexing properties, we have synthesized thiophene monomers bear-
ing different functional groups at the 3 position of the ring, in order to
study their effect on the electron density and consequently on the facil-
ity of the electropolymerization of these monomers.
RESULTS AND DISCUSSION
Synthesis of Monomers
In order to introduce complexing groups into the thiophene ring, we
have chosen to synthesize Schiff bases, esters, amides, and thiophenyl
amino acids, which are presented in Table I. The methods of synthesis
are described in detail in the experimental section.
Electropolymerization
For all the monomers synthesized, we have studied their ability to
form conducting polymer films on an electrode surface by using the
technique of Cyclic Voltammetry (CV). The device used was a clas-
sical three-electrode system, the solvent being either acetonitrile or
dichloromethane, and tetra-n-butylammonium tetrafluoroborate being
the inert electrolyte. The measurements have been realized at different

Synthesis of Functionalized Thiophenes
725
TABLE I Thiophene Monomers
Schiff bases
R
n-Pr
i-Pr
n-Bu
1
2
3
4
n-Hept
Esters
R
Me
i-Pr
n-Bu
5
6
7
Amides
R
n-Pr
i-Pr
8
9
n-Hept
10
Amino acids
R
H
OCH3
11
12
concentrations of the monomers, different scan rates, and various limits
of the oxidation potential.
Typical results are shown in Figures 1–6. It can be seen from Figure
1 that the oxidation of 2 starts at a potential of about 1.1 V, and then
the current increases without formation of a visible voltammetric peak.
For 3 (Figure 2) the oxidation potential is higher by about 50 mV; in this
case, however, the formation of a voltammetric peak at about 1.58 V is
clearly visible. Both compounds undergo irreversible oxidation, and the
oxidation products do not yield a conducting polymer deposited on the
electrode. In both cases a small reduction peak can be observed at about
0.1 V due to the presence of protons removed from these molecules.
The cyclic voltammetry curve for thiophen-3-yl-acetic acid methyl
ester 5 is shown in Figure 3. The onset of the monomer oxidation is
close to 1.19 V, and with scanning to 2.25 V the current increases rapidly
without formation of a peak. However, in the reverse cycle two reduction

726
A. Brembilla et al.
FIGURE 1 Cyclic voltammetry of N-(3-thienylmethylene)-i-propyl-1-amine 2
(0.01 M, black lines) and pure electrolyte (gray lines) in 0.1 M NBu4BF4/ CH2Cl2
solution. Scan rate: 50 mV·s−1
.
peaks can be observed at potentials of 0.12 and 1.05 V. The first one,
similar to the two compounds previously mentioned is representative
of proton reduction, while the second is connected with the reduction
of the oxidized polymer forming a layer on the electrode. During the
second voltammetric cycle, the polymer oxidation peak is visible at 1.25
V, and for each subsequent cycle, both reduction and oxidation currents
increase, indicating the increase of the thickness of the polymer layer.
The potential of the oxidation peaks is shifted with every scan toward
more positive values, which indicates a moderate conductivity of the
FIGURE 2 Cyclic voltammetry of N-(3-thienylmethylene)-n-butyl-1-amine 3
(0.01 M, black lines) and pure electrolyte (gray line) in 0.1 M NBu4BF4/ CH2Cl2
solution. Scan rate: 50 mV·s−1
.

Synthesis of Functionalized Thiophenes
727
FIGURE 3 Cyclic voltammetry of thiophen-3-yl-acetic acid methyl ester 5
(0.02 M, black lines) and pure electrolyte (gray line) in 0.1 M NBu4BF4/ CH2Cl2
solution. Scan rate: 50 mV·s−1
.
polymer layers formed. This behavior is similar to that described in the
literature for other 3-substituted thiophenes bearing carboxyl groups.11
Figure 4 shows cyclic voltammetric curves for thiophen-3-yl-acetic
acid i-propyl ester 6. This compound starts to oxidize at very high po-
tentials close to 1.9 V; even in acetonitrile, a solvent that allows extend-
ing the oxidation domain up to 2.5 V, only an unclear peak at 2.4 V is
observed. The oxidation process is irreversible, and the formation of a
conducting polymer at the electrode is not observed.
FIGURE 4 Cyclic voltammetry of thiophen-3-yl-acetic acid i-propyl ester 6
(0.01 M, black line) and pure electrolyte (gray line) in 0.1 M NBu4BF4/ acetoni-
trile solution. Scan rate: 50 mV·s−1
.

728
A. Brembilla et al.
FIGURE 5 Cyclic voltammetry of N-i-propyl-2-thiophen-3-yl-acetamide 9
(0.01 M, black lines) and pure electrolyte (gray lines) in 0.1 M NBu4BF4/ CH2Cl2
solution. Scan rate: 50 mV·s−1
.
The results of the electrochemical studies of N-n-propyl-2-thiophen-
3-yl-acetamide 8 and methyl 3-[(3-thienylacetyl)amino]propanoate 11
are shown in Figures 5 and 6, respectively. The onset of oxidation for
both compounds is visible at 1.5–1.8 V, but the process is irreversible.
In both cases the formation of conducting polymers is not observed,
possibly due to a preferential oxidation of the amide group, as suggested
by Koßmehl et al.12 In the case of 8 two very well-resolved reduction
peaks can be observed at about 0.7 and 0.05 V due to the formation of
σ-dimers and simultaneous removal of protons from these molecules.
FIGURE 6 Cyclic voltammetry of methyl 3-[(3-thienylacetyl)amino]pro-
panoate 11 (0.01 M, black lines) and pure electrolyte (gray line) in 0.1 M
NBu4BF4/ CH2Cl2 solution. Scan rate: 50 mV·s−1
.

Synthesis of Functionalized Thiophenes
729
CONCLUSION
From the figures above it can be seen that only the monomer bearing a
relatively small substituent, a methyl ester group, leads to a conducting
polymer (Figure 3). The remaining compounds do not form a conduct-
ing polymer film on the electrode surface. In this case polymerization
may occur, but the macromolecular chains obtained are not sufficiently
planar to lead to observable conducting properties.
The fact that among different members of the same series of com-
pounds (e.g., thienyl esters) only the monomer with the least volu-
minous substituent yields evidence for the formation of a conducting
polymer film indicates that the decisive factor for the electropolymer-
izability is the steric hindrance of bulky substituents and not their
electron-withdrawing properties.
A comparison of the different series of monomers indicates that the
smallest Schiff base 1 does not form conducting films, whereas methyl
ester 5 of similar size allows for polymerization. This may be due to a
higher flexibility of the ester with respect to the more rigid Schiff base.
These observations lead to the conclusion that a “dilution” of the sub-
stituent density along the macromolecular chain should be in favor of
the formation of a planar polythiophene structure and hence a signifi-
cantly higher conductivity along the chain. This can be obtained by, e.g.,
using as monomers di- or trimers of thiophene bearing only one com-
plexing function per molecule. Work in this direction is under progress.
EXPERIMENTAL
Experimental Protocols
All solvents were reagent grade and used without further purification.
Progress of the reactions and purity of the products were evaluated us-
ing thin layer silica gel chromatographic (TLC) plates (Merck, Darm-
stadt, Germany, Kieselgel 60 F254) with ethyl acetate-hexane mixtures
as eluents. Purification was carried out, when necessary, by flash sil-
ica gel column chromatography with the same eluents. Melting points
were determined with an electronic apparatus (electrothermal) and
1
have not been corrected. H NMR spectra were recorded on Bruker
DRX 400 or AM 200 spectrometers. Chemical shifts are reported in ppm
downfield from internal tetramethylsilane (TMS) and the coupling con-
stants in Hz. IR spectra were recorded on a Perkin-Elmer Spectrum
One FTIR spectrometer equipped with an Attenuated Total Reflection
(ATR) accessory. Elemental analyses were carried out on a Thermofinni-
gan FlashEA 1112 apparatus. They agree with the proposed structures,
and illustrative results are reported for some compounds.

730
A. Brembilla et al.
For the CV experiments, a three-electrode glass cell was used, with
a platinum working electrode (0.07 cm2 surface area), a platinum-
wire counter-electrode, and a Ag/Ag+ reference. Potential sweeps were
controlled by a CHI 620A potentiostat (CH Instruments, Austin,
Texas, USA). Solvents used in these studies were either anhydrous
dichloromethane or acetonitrile. Tetra-n-butyl ammonium tetrafluorob-
orate served as an inert electrolyte. The concentrations of thiophenes
that were examined varied from 0.005 to 0.1 mol·L−1; optimal results
have been obtained in the concentration range of 0.01–0.02 mol·L−1
.
Syntheses
Preparation of Schiff Bases
N-(3-Thienylmethylene)-n-propyl-1-amine (1). In a typical experi-
ment 1 eq. of 3-thiophene carbaldehyde (1.12 g, 10 mmol) was added
to 1.2 eq. of n-propylamine (0.71 g, 12 mmol) and 0.02 g of p-toluene
sulfonic acid, dissolved in 50 mL of toluene. The mixture was heated to
reflux for 3 h under stirring in a reactor equipped with a Dean-Stark
head. After cooling to r.t., the solution was extracted twice with 15 mL
of aq. NaHCO3, twice with 15 mL of sat. NaCl, and finally 3 times with
15 mL of water. The organic phase was dried over anhydrous Na2SO4.
After evaporation of the solvent, the product 1 was obtained as a
yellow liquid (1.4 g, 92%). Elemental analysis: Found: C, 62.9; H, 7.4;
1
N, 8.9; S, 20.5. Calcd. for C8H11NS: C, 62.7; H, 7.2; N, 9.1; S, 20.9. H
NMR (200 MHz, CDCl3) δ: 7.1–7.6 (m, 3H, thiophenes-H), 8.28 (s, 1H,
N CH), 3.52 (t, J = 6.9 Hz, 2H, CH2-N), 1.70 (m, 2H, CH3CH ), 0.94
2
(m, 3H, CH3). IR νmax (film, cm−1): 1641 (C N), 780 (monosubstituted
thiophene).
The following members of the series have been prepared in an anal-
ogous manner.
N-(3-Thienylmethylene)-i-propyl-1-amine (2). 1.12 g (10 mmol) of 3-
thiophene carbaldehyde, 0.78 g (12 mmol) of i-propylamine. Yield 0.8 g
1
(52%) of a light yellow oil. H NMR (200 MHz, CDCl3) δ: 7.1–7.7 (m,
3H, thiophenes-H), 8.30 (m, 1H, N CH), 3.50 (m, 1H, CH N), 1.31 (d,
J = 6.2 Hz, 6H, CH3). IR νmax (film, cm−1): 1635 (C N), 780 (monosub-
stituted thiophene).
N-(3-Thienylmethylene)-n-butyl-1-amine (3). 1.12 g (10 mmol) of
3-thiophene carbaldehyde, 0.88 g (12 mmol) of n-butylamine. Yield
1.49 g (90%) of a yellow oil. 1H NMR (200 MHz, CDCl3) δ: 7.2–7.5
(m, 3H, thiophenes-H), 8.19 (m, 1H, N CH), 3.49 (t, J = 7.0 Hz, 2H,
CH2 N), 1.61 (m, 2H, CH3CH2CH ), 1.31 (m, 2H, CH3CH CH2), 0.88
2
2

Synthesis of Functionalized Thiophenes
731
(t, J = 7.4 Hz, 3H, CH3). IR νmax (film, cm−1): 1640 (C N), 779 (mono-
substituted thiophene).
N-(3-Thienylmethylene)-n-heptyl-1-amine (4). 1.12 g (10 mmol) of
3-thiophene carbaldehyde, 1.38 g (12 mmol) of n-heptylamine. Yield
1
2.07 g (99%) of a dark yellow oil. H NMR (400 MHz, CDCl3) δ: 7.1–
7.6 (m, 3H, thiophene-H), 8.26 (m, 1H, N CH), 3.55 (t, J = 7.0 Hz,
2H, CH2-N), 1.67 (m, 2H, CH CH2N), 1.28 (br m, 8H, CH3(CH ) CH2),
2
2 4
0.89 (t, J = 6.5 Hz, 3H, CH3). IR νmax (film, cm−1): 1642 (C N), 782
(monosubstituted thiophene).
Preparation of Esters
Thiophen-3-yl-acetic Acid Methyl Ester (5). One eq. (1.42 g,
10 mmol) of 3-thiophene acetic acid was dissolved in 100 mL of methanol
containing 0.1 g of sulfuric acid as a catalyst. The mixture was refluxed
for 6 h. The methanol was removed under reduced pressure. The residue
was dissolved in 20 mL of ethyl acetate, and the solution was extracted
twice with 15 mL of aq. NaHCO3, twice with 15 mL of sat. NaCl, and
finally 3 times with 15 mL of water. The organic phase was dried over
anhydrous MgSO4. The product (1.55 g, 99%) was a viscous yellow oil.
Elemental analysis: Found: C, 54.0; H, 5.3; S, 20.2. Calcd. for
C7H8O2S: C, 53.8; H, 5.2; S, 20.5. 1H NMR (400 MHz, CDCl3) δ: 7.0–7.3
(m, 3H, thiophene), 3.65 (s, 2H, CH2), 3.62 (s, 3H, CH3). IR νmax(film,
cm−1): 1733 (ester C O), 762.
Thiophen-3-yl-acetic Acid i-Propyl Ester (6). One eq. (1.42 g,
10 mmol) of 3-thiophene acetic acid, 1.2 eq. (0.75 g, 12 mmol) of iso-
propanol, and 0.02 g of p-toluene sulfonic acid were dissolved in 100
mL of toluene. The mixture was refluxed for 6 h in a Dean-Stark reac-
tor. After cooling to r.t., the solution was extracted twice with 15 mL of
aq. NaHCO3, twice with 15 mL of sat. NaCl, and finally 3 times with
15 mL of water. The organic phase was dried over anhydrous MgSO4.
After evaporation of the solvent, the product 6 was obtained as a yel-
1
low liquid (1.2 g, 61%). H NMR (200 MHz, CDCl3) δ: 7.0–7.3 (m, 3H,
thiophene-H), 3.65 (s, 2H, CH2), 5.00 (septet, J = 6.2 Hz, 1H, CH), 1.21
(d, J = 6.2 Hz, 6H, CH3). IR νmax (film, cm−1): 1727 (ester C O), 763.
The ester 7 was obtained in a similar manner.
Thiophen-3-yl-acetic Acid n-Butyl Ester (7). One eq. (1.42 g,
10 mmol) of 3-thiophene acetic acid, 1.2 eq. (0.88, 12 mmol) of n-butanol.
Yield 1.19 g (60%) of an orange-yellow oil. 1H NMR (400 MHz, CDCl3) δ:
7.0–7.35 (m, 3H, thiophenes-H), 3.64 (s, 2H, CH2-C(O)), 4.26 (m, 2H,
CH2-O), 1.61 (m, 2H, CH3CH2CH ), 1.35 (m, 2H, CH3CH CH2), 0.93 (t,
2
2
J = 7.2 Hz, 3H, CH3). IR νmax (film, cm−1): 1730 (ester C O), 758.

732
A. Brembilla et al.
Preparation of Amides
N-n-Propyl-2-thiophen-3-yl-acetamide (8). Equimolar amounts
(typically 10 mmol) of 3-thiophene acetic acid and n-propylamine
were dissolved under vigorous stirring in a 90:10 methanol-water
mixture. After complete dissolution of the reagents, the solvents were
evaporated under reduced pressure and the residue was lyophilized
in order to eliminate residual water. The resulting ammonium salt
was then dissolved in 100 mL of toluene and the solution refluxed for
6 h in a Dean-Stark reactor. After cooling to r.t., the organic solution
was extracted twice with 15 mL of aq. NaHCO3, twice with 15 mL
of sat. NaCl, and finally 3 times with 15 mL of water. The organic
phase was dried over anhydrous MgSO4. Evaporation of the solvent
under reduced pressure yielded the crude product as a yellowish paste.
After purification on a silica-gel column with hexane/ethyl acetate
20:80 as the eluent, the amide was recovered as a slightly yellow solid.
Yield: 1.42 g (77%). Elemental analysis. Found: C, 58.7; H, 7.4; N,
1
7.2; S, 17.1. Calcd. for C9H13NO:S C, 59.0; H, 7.2; N, 7.6; S, 17.5. H
NMR (400 MHz, CDCl3) δ: 7.0–7.4 (m, 3H, thiophenes-H), 3.61 (s, 2H,
CH2-C O), 6.90 (br s, 1H, NH), 3.24 (m, 2H, CH3CH2CH ), 1.41 (m, 2H,
2
CH3CH CH2), 0.95 (m, 3H, CH3). IR νmax(KBr, cm−1): 1643 (C(O)N),
2
760.
The following members of the series have been prepared in an anal-
ogous manner.
N-i-Propyl-2-thiophen-3-yl-acetamide (9). 0.5015 g (8.5 mmol) of
i-propylamine and 1.21 g (8.5 mmol) of 3-thiophene acetic acid. 1H
NMR (200 MHz, CDCl3) δ: 7.0–7.3 (m, 3H, thiophenes-H), 3.59 (s, 2H,
CH2 C O), 5.70 (br s, 1H, NH), 3.95 (septet, J = 7.0 Hz, 1H, CH),
1.02 (d, J = 7.0 Hz, 6H, CH3). IR νmax (film, cm−1): 1555 (C O), 1641
(C(O) N), 759.
N-n-Heptyl-2-thiophen-3-yl-acetamide (10). 1.15 g (10 mmol) of i-
propylamine and 1.42 g (10 mmol) of 3-thiophene acetic acid. Yield: 1.9
1
g (79%) of a yellow-white solid. H NMR (400 MHz, CDCl3) δ: 6.9–7.4
(m, 3H, thiophene-H), 5.44 (br s, 1H, NH), 3.58 (s, 2H, CH2 C O), 3.20
(m, 2H, CH2-N), 1.78 (m, 2H, CH CH2N), 1.42 (m, 2H, CH CH2CH2N),
2
2
1.24 (br m, 6H, CH3(CH ) ), 0.87 (t, J = 6.4 Hz, 3H, CH3). IR νmax(film,
2 3
cm−1): 1553 (C O), 1643 (C N), 760.
Preparation of Amino Acids
Methyl 3-[(3-Thienylacetyl)amino]propanoate (11) and Methyl
3-{[(4-Methoxy-3-thienyl)acetyl]amino}propanoate (12). These two
compounds were prepared in the same manner: 1 eq. (typically 10 mmol)

Synthesis of Functionalized Thiophenes
733
of the corresponding 3-thiophene acetic acid (R H or OCH3), 1 eq. of
β-alanine methylester, 1 eq. of benzotriazol(tris-dimethylamino) phos-
phonium hexafluorophosphate as coupling reagent, and 3 eq. of triethyl-
amine were dissolved in 60 mL of acetonitrile. The mixture was stirred
at r.t. for 12 h. After evaporation of the solvent, the residue was redis-
solved in dichloromethane. The organic solution was extracted twice
with 30 mL of 2N hydrochloric acid, twice with 30 mL of aq. NaHCO3,
twice with 30 mL of sat. NaCl, and finally 3 times with 30 mL of wa-
ter. After removal of the solvent under vacuum, the crude product was
purified on a silica-gel column with a 20:80 hexane/ethyl acetate mix-
ture as the eluent. The final product was obtained under the form
of a viscous translucid gel (1.18 g, 52% for 11, and 1.24 g, 48% for
12).
11: Elemental analysis: Found: C, 53.3; H, 5.7; N, 5.8; S, 13.6. Calcd.
1
for C10H13NO3S: C, 52.9; H, 5.8; N, 6.2; S, 14.1. H NMR (400 MHz,
CDCl3) δ: 6.9–7.4 (m, 3H, thiophenes-H), 3.56 (s, 2H, thiophene-CH -
2
C O), 6.41 (br s, 1H, NH), 3.46 (t, J = 6.0 Hz, 2H, CH2-N), 2.51 (t,
J = 6.0 Hz, 2H, CH CH2N), 3.65 (s, 3H, OCH3). IR νmax (film, cm−1):
2
1732(C O), 1645 (N C), 762 (monosubstituted thiophene).
12: 1H NMR (400 MHz, CDCl3) δ: 6.1–7.9 (m, 2H, thiophenes-H), 3.81
(s, 3H, OCH3), 3.58 (s, 2H, thiophene-CH -C O), 7.74 (br s, 1H, NH),
2
3.54 (t, J = 6.2 Hz, 2H, CH2-N), 2.50 (t, J = 6.2 Hz, 2H, CH CH2N),
2
3.57 (s, 3H, C(O)OCH3). IR νmax (film, cm−1): 1732(C O), 1646 (N C),
1553 (3,4-disubstituted thiophene).
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of Conducting Polymers, 2nd ed. (Marcel Dekker, New York, 1998).
[2] U. Mitschke and P. Ba¨uerle, J. Mater. Chem., 10, 1471 (2000).
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