Synthesis and characterization of oligo- and crown ether-substituted polythiophenes - A comparative study

Article abstract of DOI:10.1039/a902823d

The synthesis of two series of thiophenes substituted with crown and oligoether groups either via isolating oxaalkyl chains (2, 7-11) or in direct π-conjugation (4, 12-15) is described. Electrooxidative polymerization leads to the corresponding crown and oligoether-functionalized polythiophenes P2, P7-P11, and P4, P12, respectively. Their electrochemical and spectroscopic properties depend on the length of the spacer and the type of the ether unit. The polymers reveal a high mean conjugation. A specific and strong influence of alkali ions on the electrochemical behavior is found for several polymers. The selectivities correspond to the match of the cation size without solvent shell and the inner diameter of the crown ether units. Spectroelectrochemical experiments corroborate that the changes in redox properties are due to a hindered diffusion of the counter anions into the film when the polymer is oxidized. Due to the structural variation novel materials sensitive to different cations are obtained. Importantly, in these conjugated polymers chemical information which corresponds to a selective host-guest interaction of the alkali metal cations and the ether units is transduced into the change of an electrical signal.

Full text of DOI:10.1039/a902823d

J O U R N A L O F
Synthesis and characterization of oligo- and crown ether-substituted
polythiophenes—a comparative study
Stefan Scheib† and Peter Ba¨uerle*
Abteilung Organische Chemie II, Universitat Ulm, D-89081 Ulm, Germany.
¨
C H E M I S T R Y
E-mail: peter.baeuerle@chemie.uni-ulm.de
Received 9th April 1999, Accepted 2nd June 1999
The synthesis of two series of thiophenes substituted with crown and oligoether groups either via isolating oxaalkyl
chains (2, 7–11) or in direct p-conjugation (4, 12–15) is described. Electrooxidative polymerization leads to the
corresponding crown and oligoether-functionalized polythiophenes P2, P7–P11, and P4, P12, respectively. Their
electrochemical and spectroscopic properties depend on the length of the spacer and the type of the ether unit. The
polymers reveal a high mean conjugation. A specific and strong influence of alkali ions on the electrochemical
behavior is found for several polymers. The selectivities correspond to the match of the cation size without solvent
shell and the inner diameter of the crown ether units. Spectroelectrochemical experiments corroborate that the
changes in redox properties are due to a hindered diffusion of the counter anions into the film when the polymer is
oxidized. Due to the structural variation novel materials sensitive to different cations are obtained. Importantly, in
these conjugated polymers chemical information which corresponds to a selective host–guest interaction of the alkali
metal cations and the ether units is transduced into the change of an electrical signal.
Conducting polymers with various covalently attached func-
tional groups have become more and more prominent in recent
years. On the one hand, effective synthetic strategies are now
available;1 on the other hand, it is a challenge to address and
influence the electronic properties of the conjugated backbone
from the outside via specific interactions of covalently attached
functional groups with external chemical or physical stimuli.2
A very promising approach to this goal is to use conducting
polymers bearing molecular recognizing groups in which very
selective host–guest interactions modulate, switch, and amplify
the electron transport properties of the conjugated chains.
Very recently, several attempts to realize this concept have
been demonstrated. These include various oligooxyethylene-
substituted polythiophenes,3 crown ether-substituted poly-
thiophenes4 and corresponding model oligothiophenes,5 and
aza-crown ether-substituted polypyrroles.6 More complicated
systems include calix[4]arene-substituted polythiophenes,7 or
metallorotaxane receptor sites attached to thiophene–pyridine
copolymers.8 Due to electrostatic and/or conformational per-
turbations of the conjugated backbone, in most cases, conduc-
tivity, electrochemical and optical responses may be influenced
by the complexation of metal ions.
Approaches to exploit the unique but more complex recog-
nizing properties of biomolecules in combination with con-
ducting polymers have recently been described. Di- and
tripeptides, known to be specifically recognized and bound by
appropriate proteins, have been covalently linked to poly-
pyrrole.9 Single DNA-nucleobases linked to a polythiophene
show that the specific recognition of a complementary base
results in the modulation of the electronic properties of the
polymeric backbone.10 Even more intriguing, oligonucleotide-
functionalized polypyrroles11 or polythiophenes12 respond
specifically to complementary oligonucleotide sequences and
represent very promising components for amperometric DNA-
sensors.13 The attachment of biotin at a water-soluble poly-
alkoxythiophene which specifically interacts with the protein
in which the complexation/decomplexation process allows an
externally induced switching between the ON/OFF states, i.e.
in field effect transistors.15 Due to the stronger ion–dipole
interactions with metal cations, crown ether-functionalized
materials are particularly interesting for these applications,
since it could be successfully demonstrated that it is possible
to transduce chemical information into the change of an
electrical signal.3–7 In this respect, by systematic variation, we
recently realized the synthesis of different thiophenes (1–3)
with 12-crown-4-ether linked to the heterocycle via a non-
conjugated oxaalkyl chain.4a Later on we synthesized a second
series of thiophenes (4–6) in which the crown ether units are
in direct p-conjugation (Scheme 1).4f Corresponding poly-
thiophenes formed from derivatives of both classes (P2, P4,
where P stands for polymer) showed selective and strong
changes in their electrochemical behavior in the presence of
alkali metal ions.
On the basis of these results we now present the synthesis
of a series of crown ether- and oligo ether-substituted bithio-
phenes 7–11 which are directly comparable to compounds 1–3
and in which the oligoether or crown ether units are attached
to the bithiophene unit via an oxaalkyl spacer. Additionally
a series of related crown ether- and oligoether-substituted
dialkoxythiophenes 12–15 were synthesized which are compar-
able to thiophenes 4–6 (Scheme 2). Furthermore, the electro-
chemical polymerization and the electrochemical behaviour of
the corresponding polymers in various alkali ion electrolyte
solutions are shown. (Monomer) structure–(polymer) property
relationships are deduced and clearly show how the steric
demand and/or the polarity of the side chain influences the
polymerization, the electrochemical, and the spectroscopic
properties of the polymer formed. On the basis of our results
we discuss the observed alkali metal ion sensitivity and selec-
tivity of the different polymers which support our earlier
proposed model of a potential barrier.4a,f
avidin results in
complexation.14
Selective host–guest interactions in combination with con-
ducting polymers may be exploited in (iono-)electronic devices
a
color change in solution upon
Results and discussion
Syntheses of ether-substituted thiophenes 7–15
The synthesis of the bithiophene key building blocks 3-(v-
bromoalkyl)-2,2∞-bithiophenes 20 (n=5)4a and 21 (n=10)
started from the corresponding 3-(v-bromoalkyl)thiophenes
†Present address: Cilag AG, CH-8205 Schaffhausen, Switzerland.
J. Mater. Chem., 1999, 9, 2139–2150
2139

Scheme 1
Scheme 2
2140
J. Mater. Chem., 1999, 9, 2139–2150

16 (n=5)16 or 17 (n=10)16 which were selectively brominated
in the 2-position with N-bromosuccinimide (NBS) in dimethyl-
formamide (DMF)17 forming the monobromo compounds 18
(n=5) and 19 (n=10) in 80 and 42% yield, respectively. Via
nickel-catalyzed cross-coupling of thiophenes 18 and 19 with
2-thienylmagnesium bromide 3-alkyl-2,2∞-bithiophenes 20 (n=
5) and 21 (n=10) were obtained analytically pure after
repeated distillation in 81 and 32% yield (Scheme 3a). The
various novel ether-functionalized bithiophenes 7–11 were
synthesized via phase-transfer reaction of bithiophenes 20 and
21 with the respective crown ether or oligoether alcohols.
Chromatographic work-up of the raw material led in all cases
to analytically pure compounds 7–11 as slightly yellow oils in
40–72% yield (Scheme 3b). Synthesis of the crown ether-
substituted monothiophenes 4, 12 and 14 was accomplished
following the procedure of Sone et al.18 Thus, 2,5-bis(ethoxy-
carbonyl)-3,4-dihydroxythiophene 22,19 one of the few stable
dihydroxythiophenes, was alkylated with the ditosylates of
tri-, tetra-, or pentaethylene glycol in dry acetonitrile with
potassium fluoride as base in the case of thiophene 12 or
cesium fluoride20 for thiophenes 4 and 14. The resulting crown
ether-substituted bis(ethoxycarbonyl) thiophenes were sapon-
ified to the corresponding diacids which subsequently were
heated under reduced pressure to eliminate carbon dioxide
with formation of the monothiophenes 4, 12 and 14 (45, 47,
and 35% yield). The novel oligoether-substituted thiophenes
13 and 15 were prepared by similar procedures. Reaction of
ethylene glycol monomethyl ether monotosylate with 2,5-
bis(ethoxycarbonyl)-3,4-dihydroxythiophene 22 in dry DMF
with potassium carbonate as base21 led in 87% yield to the
bis(ethoxycarbonyl)thiophene 23 which could be saponified
and decarboxylated to the oligoether thiophene 13 in 38%
yield. Bis(ethoxycarbonyl)thiophene 24 was prepared by the
similar reaction of diethylene glycol monomethyl ether mono-
tosylate and 2,5-bis(ethoxycarbonyl)-3,4-dihydroxythiophene
22 in dry acetonitrile with potassium fluoride as base in 31%
yield after distillation. Saponification and decarboxylation led
to oligoether thiophene 15 in 18% yield (Scheme 3c). 3-
Dodecyl-2,2∞-bithiophene 25 was synthesized separately22 and
is used here as an alkyl-substituted reference compound.
Electrochemistry of the crown ether- and oligoether-substituted
bithiophenes 7–11
The electrochemical characterization of the bithiophenes 7–11
expectedly revealed an irreversible oxidation wave of the
bithiophene unit in the cyclic voltammogram (CV). All peak
potentials are essentially the same and are in a range of E =
pa
0.84–0.88 V vs. Fc/Fc+ (Table 1). The ether and crown ether
moieties are stable and electrochemically inactive in the poten-
tial range examined.23 All electrochemical characterizations
and polymerizations were carried out in dry acetonitrile
(MeCN) with tetrabutylammonium hexafluorophosphate
(TBAHFP) (0.1 M) as supporting electrolyte. All 3-substituted
bithiophenes 2, 7–11 and 25 could be polymerized to the
corresponding poly(bithiophenes) P2, P7–P11, and P25 by
means of a potentiodynamic oxidation. Potentiostatic or gal-
vanostatic polymerizations led to the same quality of films.
The conditions employed for the potentiodynamic polymeriz-
ations were optimized and are given in Table 2. Although
every monomer bears the same electroactive bithiophene unit,
it was found in this series that the various functionalized
bithiophenes have different tendencies to polymerize. Thus,
oligoether 11 bearing two bithiophene units and reference
compound 25 showed excellent film forming properties and
growth rates. However, the 12-crown-4- and oligoether-substi-
tuted derivatives 2, 7 and 8 polymerized somewhat more slowly
and twice as many cycles were necessary to deposit about the
same amount of polymer on the working electrode. The
quantity of polymer deposited can be estimated from the CV
taken in an electrolyte free of monomer by the charge which
is reversibly exchanged in the oxidation/reduction cycle.
However, there are evidently only small differences between
the polymerization ability of bithiophenes 2 and 7 in which
the spacer between the conjugated backbone and the crown
ether unit is varied (n=5, 10) and between compounds 2 and
8 in which the pentamethylene spacer remains identical (n=
5). Due to much more steric hindrance and in contrast to
bithiophenes 2 and 7, 18-crown-6-substituted bithiophenes 9
and 10 showed only moderate film forming behavior. During
the polymerization of these compounds highly colored blueish–
greenish oligomeric products were formed which did not
Scheme 3
J. Mater. Chem., 1999, 9, 2139–2150
2141

Table 1 Electrochemical and spectroscopic data of the ether-substituted bithiophenes 2, 7–11 and 25 and the corresponding polymers P2,
P7–P11, P25
(M)/(P)
E
(M)/Va
E
1 (P)/Va
pa
E
2 (P)/Va
l
(M)/(P)/nm
E (P)/eV
pa
pa
max
g
2/P2
0.85
0.86
0.86
0.88
0.88
0.84
0.85
0.07
0.19
0.11
0.14
0.20
0.10
0.38b
0.45
0.48
0.45
0.42
0.48
0.26
0.45
295/538
294/524
295/508
295/477
294/512
295/482
295/506
1.91
1.90
1.98
2.04
1.93
1.98
1.97
7/P7
8/P8
9/P9
10/P10
11/P11
25/P25
aMeCN–TBAHFP, 0.1 M, 100 mV s−1, all potentials vs. Fc/Fc+. bSecond scan of characterization.
Table 2 Polymerization conditions for the bithiophenes 2, 7–11 and 25
Polymerization
tendencyc
(M)
Concentration/mol L−1
Potential range/Va
Number of scans
Charge/mCb
2
7
1.4·10−2
6.1·10−3
1.3·10−2
5.5·10−3
6.1·10−3
1.0·10−3
5.1·10−3
−0.36–0.89
−0.36–0.89
−0.36–0.94
−0.36–0.99
−0.36–0.99
−0.36–0.89
−0.36–0.81
20
10
40
80
80
10
10
0.90
0.58
0.59
0.60
1.17
1.04
1.00
++
++
++
+
8
9
10
11
25
+
+++
+++
aMeCN–TBAHFP, 0.1 M, 100 mV s−1, all potentials vs. Fc/Fc+. bReversibly exchanged charge of the conducting polymer at 100 mV s−1 scan
speed. This charge corresponds to the amount of electroactive polymer deposited on the working electrode. c+++ very good; ++
good;+moderate.
adhere to the electrode surface and diffused away into the
solution. In the case of the other bithiophenes almost no
coloring of the electrolyte was observed. Like bithiophene 2
all new ether-substituted bithiophenes 7–11 and the reference
compound 25 form the corresponding polymers P7–P11 and
P25. Thus in general, the 3-substituted 2,2∞-bithiophene unit
allows the use of sterically very demanding side groups and
therefore proved to be an ideal monomer for the formation of
functionalized conducting polythiophenes which we could also
confirm in other examples.24
The poly(bithiophenes) P2, P7–P11 and P25 were charac-
terized electrochemically in an electrolyte free of monomer.
The electrochemical properties of the polymers were deter-
mined from at least 10 polymer coated electrodes prepared
under the same polymerization conditions. The resulting CVs
for all polymers are depicted in Fig. 1. It should be pointed
out that even under identical polymerization conditions the
oxidation potentials of the same polymer can differ in a small
potential range (Table 1). The shape of all reversible CVs is
typical for polyheterocycles and includes two maxima in the
oxidative part and less pronounced broad peaks in the
reductive part. For poly(bithiophenes) P2 and P8 the first
oxidation wave is sharp and well pronounced whereas the
second one is very broad. For polymers P7, P9–P11 the
opposite behavior is observed. The lowest oxidation potential
was obtained for poly(bithiophene) P2 (E 1=0.07 V vs.
Fig. 1 Cyclic voltammograms of the polymers P2, P7–P11, and P25
in MeCN–TBAHFP (0.1 M, 100 mV s−1). The first successive three
scans of the characterization are shown.
pa
Fc/Fc+) including the short pentamethylene spacer. Gradually
increasing peak potentials are found for poly(bithiophenes)
P11 (E 1=0.10 V vs. Fc/Fc+), P8 (E 1=0.11 V vs. Fc/Fc+),
pa
pa
and P9 (E 1=0.14 V vs. Fc/Fc+). Polymers P7 (E 1=0.19 V
Spectroscopic characterization of the poly(bithiophenes) P2,
P7–P11, and P25
pa
pa
vs. Fc/Fc+) and P10 (E 1=0.20 V vs. Fc/Fc+) which include
pa
the longer decamethylene spacer show the most positive peak
potentials in this series. Compared to the reference polymer
Absorption data are sensitive parameters for structural and
conformational effects in conjugated p-systems. Comparison
of longest wavelength absorptions of the polymers allows
determination of the influence of the side chain on the confor-
mation of the conjugated backbone.26 The spectroscopic
characterization of the poly(bithiophenes) in different oxi-
dation states was performed in a special spectroelectrochemical
cell.27 The monomers were directly polymerized via potentio-
P25 (E 1=0.38 V vs. Fc/Fc+) these values are surprisingly
pa
low. Possibly a polar side chain including oxygen atoms (P2,
7–11) lowers the oxidation potential due to the higher ionic
conductivity of the polyether groups.25 This allows easier
diffusion of the counter ions into the film which are needed
for the compensation of the positive charges in the oxidized
polymer backbone.
2142
J. Mater. Chem., 1999, 9, 2139–2150

dynamic polymerization onto a polished platinum electrode
which afterwards was directly used as the working electrode
in the spectroelectrochemical cell. The absorption spectra of
the polymers were recorded through a thin layer of electrolyte
with the aid of wave guides. By using this technique the
polymers for both the electrochemical and the spectroscopic
investigations were prepared in the same way and should
therefore have the same characteristics. The absorption maxi-
ments were performed and the remaining average electro-
activity is given after 50 scans (Table 3).
The experimental error of these data lies in between 5%
and therefore the results represent a general trend. Thus, the
electrochemical behaviour of 12-crown-4-substituted poly(bi-
thiophenes) P2 and P7 and oligoether-substituted poly(bi-
thiophene) P8 is strongly influenced in the presence of alkali
metal ions. In the case of the other ether-substituted poly(bithio-
phenes) P9, P10, P11, and expectedly of the reference polymer
P25 only marginal or no changes were observed. The electro-
chemical behavior of the polymers P2 and P7 is most strongly
influenced by lithium ions and less by sodium or potassium ions,
whereas the electroactivity of the oligoether-substituted polymer
P8 is most changed by sodium ions. In polymer P7 in which the
crown ether unit is separated from the conjugated backbone by
the longer decamethylene spacer the electroactivity drops to
about one fifth of the original value in the presence of lithium
ions. In polymer P2 containing the shorter spacer 40% of the
electroactivity rests. Comparison of the inner diameter of 12-
mum of 12-crown-4-substituted bithiophenes P2 (l
=
max
538 nm, E=2.30 eV) is at lowest energy in this series which
indicates in accordance with the electrochemical measurements
that this polymer has the highest effective conjugation.
According to the spectroscopic data of the other polymers
under investigation, the degree of conjugation should decrease
in the order P2 > P7 (l =524 nm) > P10 (l
max max
512 nm) > P8 (l =508 nm) > P25 (l =506 nm) > P11
max max
(l =482 nm) > P9 (l =477 nm). In Table 1 additionally
=
max
max
band gaps E are taken into account which were determined
g
from the absorption spectra and which show the same tend-
˚
˚
crown-4 (1.2–1.5 A)30 with the diameter of lithium ions (1.36 A
in crystals)30 shows the perfect match of the lithium ion with the
cavity of 12-crown-4. Poly(bithiophene) P8 comprising five
oxyethylene units in the spacer is selective for sodium ions and
the electroactivity is reduced to 35%. In the presence of lithium
or potassium ions in either case the electroactivity is reduced to
58%. However, the selectivity of the non-cyclic oligoether poly-
mer P8 is expectedly smaller than that of the crown ether
polymers P2 and P7. Finally, 18-crown-6-polymer P9 exhibits a
small preference for the complexation of potassium ions, whereas
lithium and sodium ions do not alter the electrochemical
response of the polymer. Also in this case the size of the
ency. Obviously, long and more flexible spacers as included in
P7, P10, P8, and P25 are more favorable for a planarized
conjugated backbone than bulky 18-crown-6 units (P9) or the
bridging of two bithiophene units (P11). The steric repulsion
of the 18-crown-6 units in poly(bithiophene) P9 induces
conformational changes in the polymer and leads to distorsions
of the thiophene rings.
So far only a few examples of 3-substituted poly(2,2∞-
bithiophenes) are known which were polymerized by electro-
chemical or chemical methods and cast into films on ITO
electrodes from solution. Thus, the dodecyl (l =528 nm28)
max
and the octyl derivative (l =525 nm29) exhibit absorptions
max
˚
potassium ion (2.66 A)30 matches with the cavity of the crown
in the same range as our oligoether-substituted polymers. Since
˚
ether unit (2.6–3.2 A).30 Despite comprising crown or oligoether
the steric demand of the crown ether units is higher than that
of an alkyl side chain, nevertheless in our cases functionalized
poly(bithiophenes) with high conjugation are obtained.
Evidently, low degrees of irregular couplings are included in
the polymers which then result in relatively low steric inter-
actions of the side chains.
units poly(bithiophenes) P10 and P11 are not sensitive to alkali
ions. For each polymer the relative selectivity to either cation
can be determined. In this respect, polymer P7 (Li+5Na+5K+=
4.551.051.5) shows the highest discrimination and in comparison
to the least recognized sodium ions (set to 1.0) lithium ions are
better recognized by a factor of 4.5, potassium ions by a factor
of 1.5. Thus, in comparison to the previously synthesized poly-
mer P2 (Li+5Na+5K+=2.051.051.1), due to the elongation of
the oxaalkyl chain in polymer P7 a strong enhancement of the
selectivity was found (Table 3).
Influence of alkali metal ions on the electrochemical behavior of
poly(bithiophenes) P2, P7–P11, and P25
Complexation of cations in crown ether-substituted conducting
polymers leads to strong changes of the electrochemical behav-
iour.3–7 Especially in the case of poly(bithiophene) P2 selective
and strong changes in the CV were found upon complexation
with alkali metal ions.4a The mechanism of how the host–
guest-interaction is transformed into the change of the electro-
chemical signal is not well understood, since the complexing
crown ether units in this material are separated by an isolating
oxaalkyl chain from the electroactive conjugated backbone.
Thus due to the structural variation, the electrochemical
characterization of this series of crown ether- and oligoether-
substituted poly(bithiophenes) P2, P7–P11, and reference
polymer P25 in the presence of alkali ions should give more
insight into this subtle process. For polybithiophene P2 we
recently found that even very low concentrations (c∏1×10−4
mol L−1) of especially lithium cations affect the electrochemi-
cal response of the polymer.4a In this investigation, the freshly
prepared poly(bithiophenes) P2, P7–P11, and P25 were
characterized by multisweep CVs in MeCN containing either
0.1 M TBAHFP, LiClO , NaClO , or KPF . The presence of
Bithiophene monomers 2, 8, and 11 were also polymerized
in electrolytes which already contained alkali ions. No differ-
ence in the polymerization tendency was found for bithio-
phenes 2 and 8 in MeCN–LiClO (0.1 M). In comparison to
4
the polymers obtained without alkali ions the resulting poly-
mers P2 and P8, however, reveal peak potentials shifted to
positive values (DE =50–160 mV) and longest wavelength
p
absorptions shifted to higher energies (Dl =17–30 nm).
max
Further addition of alkali ions to the electrolyte does not lead
to further changes of the electronic properties. These values
approximately correspond to those which are obtained when
the polymers are polymerized in MeCN–TBAHFP and alkali
ions are added afterwards. In contrast, in the case of bis-
bithiophene oligoether 11 which was polymerized in the pres-
ence of Li+, Na+, and K+ polymers P11 with increased
conjugation are obtained. In the CVs peak potentials were
found to be more negative (DE =20–40 mV) and in optical
p
measurements absorptions were red-shifted (Dl
=
max
22–29 nm). We explain this with a preorganization of the
bithiophene units which takes place in the presence of alkali
ions. Evidently, due to this template effect polymers with a
larger conjugated chain length were formed.
4
4
6
alkali metal ions in the latter electrolytes led for various
polymers to changes in the CV. Besides the shift of the first
oxidation peak to more positive potentials, a decrease in
electroactivity was observed. By integrating the areas under
the redox curves the change in electroactivity can be relatively
evaluated. The value obtained for each polymer in the alkali
ion-free electrolyte was set to 100%. For each polymer and
each electrolyte solution at least five independent measure-
How does the remote host–guest-interaction influence the
electronic properties of the conjugated backbone?
The electrochemical investigation of the oligo- and crown
ether-functionalized poly(bithiophenes) unequivocally proved
J. Mater. Chem., 1999, 9, 2139–2150
2143

Table 3 Remaining electroactivity (in percent) of poly(bithiophenes) P2, P7–P11, P25 in different electrolyte solutions (MeCN–salt, 0.1 M,
100 mV s−1)
Selectivity
(Li+5Na+5K+)a
(P)
LiClO (%)
NaClO (%)
KPF (%)
Influence
4
4
6
P2
41
22
58
100b
90
100b
100
83
100b
35
100b
100
100b
100
77
66
58
75
96
100b
88
Li+&K+≥Na+
2.051.051.1
4.551.051.5
1.051.851.0
1.051.051.3
1.151.051.0
1.051.051.0
1.051.051.1
P7
Li+&K+>Na+
P8
P9
P10
P11
P25
Na+>Li+, K+
K+>Li+, Na+
—
—
—
aThe selectivities were calculated by setting the least recognized ion to 1.0. bValues were little higher than this of the reference polymer.
that in the case of polymers P2, P7–P9 a host–guest-interaction
occurring at a remote molecular recognizing group affects
changes in the electronic properties of the conjugated back-
bone. Thus, in these materials chemical information is trans-
formed into the change of an electrochemical response.
Secondly, depending on the structure of the (crown) ether side
chain a selectivity and preference were found for those cations
whose sizes match the diameter of the crown ether unit. In
the following, we will discuss possible mechanisms. The general
trend found in complexation studies of 12-crown-4 derivatives
in solution is that sodium and potassium ions are more
strongly bound than lithium ions. Usually these measurements
are conducted in water or methanol in which the lithium ion
has a large solvent shell. This behavior is distinctly different
in MeCN in which the solvent shell consists only of nine
atoms instead of 21 atoms when water is used as solvent.3c,e
It was proposed earlier4a,f that if the complexation occurs in
a polymer matrix, the ions strip off their solvent shell when
entering the film and diffusing into the polymer matrix. Thus,
in this case only the effective radii of the metal ions are
important for complexation. This argument corresponds to
the behavior of the ether-functionalized poly(bithiophenes)
under investigation, and thus their selectivity might be gov-
erned by the match of crown ether radius and solvent-free size
of the metal cation. It was also concluded from these experi-
ments, that upon complexation of metal ions in ether units an
electrostatic potential barrier in the polymer film is formed.
This potential barrier then renders the diffusion of additional
counter ions which are necessary for charge compensation to
and into the positively charged oxidized polythiophene back-
bone more difficult. Thus, as the oxidation of the polymer is
more and more shifted to positive potentials, the more metal
cations are complexed in the film.4a,f Another explanation was
recently introduced for the similar electrochemical behaviour
of aza crown ether-functionalized polypyrroles. Complexation
of cations in the crown ether units could lead to sterically
forced twists of the thiophene units and therefore to a decrease
in conjugation.6 If this argument holds, in optical spectra the
diminution of conjugation length should result in a hypso-
chromic shift of the longest wavelength absorption. In this
respect, in a spectroelectrochemical experiment we coated
electrodes with poly(bithiophenes) P2 or P8 which were cycled
in alkali ion containing electrolytes. Surprisingly, no significant
changes in the absorption spectra could be observed. For
poly(bithiophene) P2 only a slight hypsochromic shift of the
longest wavelength absorption (Dl=7–9 nm) was found after
that the amount of polymer deposited and the morphology of
the film, which itself is strongly dependent on the film thickness,
play a crucial role for the effects observed. Smaller changes in
the electrochemical signals are observed for thicker films,
which also indicates that diffusional processes play a crucial
role.
However, the diffusion of ions in a polymer matrix is a
complex overall process in which either anions are expelled or
cations diffuse into the matrix. Additionally the diffusion of
solvent molecules and ion contact pairs can occur so that the
polymer shows complex ion exchange properties. The size of
the ions and the interactions of the ions with the polymer
influence the speed of diffusion. Taking into account that these
processes are also important for the crown ether-functionalized
poly(bithiophenes), the proposed model that an electrostatic
potential barrier due to the complexed crown ether units
hinders diffusion of the counter anions in the film is further
supported.4a,f After immersion of a poly(bithiophene) coated
electrode which was prepared in MeCN–TBAHFP into a
solution of an alkali metal salt in MeCN, the alkali cations
can spontaneously diffuse to a certain extent into the polymer
matrix and become complexed by the crown ether units.
Therefore, a Donnan potential31 is built up that hinders further
diffusion of anions into the film during the first oxidation/
reduction cycle of the poly(bithiophene). The formation of
the Donnan potential which is greater for cations with higher
charge5radius ratios also explains the selectivity of poly(bi-
thiophenes) for lithium ions due to their higher diffusion
coefficients leading to a greater incorporation in a given time.
The observed current in the first CV is significantly lower than
the current observed in the CV measured in an alkali ion free
electrolyte. During the reduction half cycle more cations diffuse
into the polymer film and saturate most of the complexation
sites available. The subsequent CVs show a further strongly
reduced electroactivity (Fig. 2). The decrease in electroactivity
50 scans in MeCN–LiClO . For oligoether polymer P8 exactly
4
the same maximum was detected after cycling in an MeCN–
NaClO -electrolyte. Although in these experiments thicker
4
polymer films had to be used, these results clearly suggest that
the change in electrochemical behavior of these polymers upon
complexation is due rather to electrostatic and diffusional
effects of the counter anions than to steric constraints which
would reduce the mean conjugation of the backbone. However,
thickness dependent electrochemical measurements showed
Fig. 2 Multisweep cyclic voltammogram (50 scans) of polymer P2 in
MeCN–TBAHFP (left). Multisweep cyclic voltammogram (3 scans)
of polymer P2 in MeCN–TBAHFP* (0.1 M, 100 mV s−1), 1st scan
in MeCN–LiClO **, and 2–50th scan in MeCN–LiClO *** (0.1 M,
100 mV s−1, each fifth scan is shown) (right).
4
4
2144
J. Mater. Chem., 1999, 9, 2139–2150

Table 4 Polymerization conditions of alkoxythiophenes 4 and 12–15
Polymerization
tendencyb
(M)
Concentration/mol L−1
Potential range/Va
Number of scans
Charge/mC
4
12
13
14
15
2.0·10−2
1.0·10−3
0.1
0.1
0.1
−0.36–1.14
−0.36–1.09
−0.36–1.54
−0.36–1.54
−0.36–1.54
20
10
150
20
4.03
3.24
—
—
—
++
+++
—
—
—
20
aMeCN–TBAHFP, 0.1 M, 100 mV s−1, all potentials vs. Fc/Fc+. b+++ very good; ++ good;—no polymerisation.
is strongest for 12-crown-4 substituted poly(bithiophenes) P2
and P7 in lithium ion electrolyte solution. A change in
electroactivity is observed when the diffusion of ions, which is
crucial for the charge transport in a conducting polymer, is
retarded or prevented by the complexed ether moieties.
crown-4 thiophene 12 a clear trace-crossing is observable
which points to fast formation of oligomeric or polymeric
material on the electrode or nearby. In the following scans
new reversible redox waves at lower potentials are formed
whose peak currents rapidly increase. This is a typical behavior
indicating increasing amounts of polymer formed on the
electrode. For 15-crown-5 monothiophene 4 the formation of
polymer is observed as well but the increase of the waves in
the CVs resulting in the formation of polymer on the electrode
is lesser although a higher monomer concentration and a
slightly extended potential range were applied for polymeriz-
ation (Table 5). Probably due to steric reasons the 18-crown-
6 monothiophene 14 showed no redox waves at more negative
potentials and could not be polymerized. This is also true for
the oligoether thiophenes 13 and 15 in which the acyclic
substituents have a much higher conformational flexibility
preventing the polymerization through steric repulsion of the
radical cations.
Electrochemistry of the 3,4-dialkoxy-substituted thiophenes 4,
12–15
All 3,4-dialkoxy-substituted monothiophenes 4 and 12–15
showed the expected irreversible oxidation peaks in the same
potential range (E =0.98–1.05 V vs. Fc/Fc+, Table 4). Due
pa
to the strong electron-donating effect of the oxygen substitu-
ents these potentials are dramatically lower than for alkylthio-
phenes and comparable to those of 3,4-ethylenedioxy-
thiophene32 and other alkoxy-substituted thiophenes.33 In
potentiodynamic polymerization experiments, 12-crown-4
thiophene 12 and 15-crown-5 thiophene 4 formed stable poly-
mers. All other monomers (13–15) did not lead to adhering
films on the electrode even at high monomer concentrations
(0.1 M) and relatively high applied oxidation potentials
(EÁ1.54 V). Since the smaller 12-crown-4 thiophene 12 poly-
merizes much faster than the bulkier 15-crown-5 thiophene 4,
the inhibition of the polymerization of the other monomers
can be attributed to the steric influence of the ether moieties
directly attached to the b-positions of the thiophene ring. This
can clearly be seen in the multisweep CVs of the crown ether-
substituted monothiophenes 4, 12 and 14 which are depicted
in Fig. 3. During the first scan in the polymerization of 12-
The polythiophenes P4 and P12 were electrochemically
characterized in an electrolyte free of monomer. The oxidation
of the 12-crown-4 polythiophene P12 starts indeed at a very
low potential of E #−0.4 V vs. Fc/Fc+ and is followed by
pa
a wave with an oxidative peak at E #0.44–0.54 V vs. Fc/Fc+.
pa
The CV of the 15-crown-5 polythiophene P4 shows a sharp
increase of the current also beginning at very negative poten-
tials (E #−0.2 V vs. Fc/Fc+) with a sharp first oxidation
pa
peak at E =−0.05 V vs. Fc/Fc+ proceeding into a broad
pa
plateau (Fig. 4). Both polymers therefore should have a rela-
tively long conjugated chain length. The absorption spectra of
both polymers P4 (l =601, 549, 520 nm) and P12 (l
=
max
max
607, 556, 520 nm) in their neutral state are quite similar and
the absorption maxima lie in the range of other 3,4-dialkoxy-
substituted polythiophenes such as poly(3,4-ethylenedioxy-
thiophene) (l =630 nm),32 poly(3,4-propylenedioxythi-
max
ophene) (l =613 nm),32 and poly(3,4-dimethoxythiophene)
max
(l =598 nm).33b The absorption maximum of 12-crown-4
polythiophene P12 is slightly red-shifted (Dl=7 nm) compared
max
to that of 15-crown-5 polythiophene P4 indicating that the
thiophene rings are a little twisted in the latter case due to the
sterically more demanding crown ether moieties. A band gap
of about E =1.85 eV was estimated for both polymers.
g
Additionally, due to vibronic couplings both novel polymers
exhibit an unusually pronounced fine structure of the p–p*-
transition band. This indicates a rigid polymer,34 with a high
degree of a linear and regular structure. Spectroelectrochemical
experiments on both polymers clearly reveal succesive intercon-
version of the reddish violet neutral form into the blue oxidized
conducting form. A weak band at l #950–960 nm is at
max
first formed upon oxidation which at a higher oxidation level
changes into a very broad absorption band with a maximum
in the NIR-regime at l >1600 nm, typical for metallic
max
conduction.
In comparison to the monothiophenes 4, 12–15, electro-
chemical characterization of both polymers P4 and P12 in the
presence of alkali metal ions was undertaken in an electrolyte
containing 0.1 M of the alkali metal ion. For the monomers
in solution an irreversible oxidation peak is found. For 12-
Fig. 3 Comparison of (multisweep) cyclic voltammograms (20 scans)
during the polymerization of bithiophenes 4 (c=1 mmol L−1), 12 (c=
0.02 mol L−1) (first scan top left; 20th scan top right), 14 (c=0.1 mol
L−1) in MeCN–TBAHFP, 0.1 M, 100 mV s−1; every 2nd scan shown.
crown-4 thiophene 12 (DE =−6/18/18 mV; Li+/Na+/K+)
pa
J. Mater. Chem., 1999, 9, 2139–2150
2145

Table 5 Electrochemical and spectroscopic data of the ether-substituted thiophenes 4, 12–15 and the corresponding polymers P4 and P12
(M)/(P)
E
(M)/Va
E
1 (P)/Va
pa
E
2 (P)/Va
l
(M)/(P)/nm
E (P)/eV
pa
pa
max
g
4/P4
12/P12
13
0.98
1.00
1.01
1.04
1.05
−0.08
0.15–0.25b
0.44–0.54b
—
—
—
256/520, 549, 601
255/520, 556, 607
1.85
1.85
—
—
—
−0.05–0.10
—
—
—
14
—
—
15
aMeCN–TBAHFP, 0.1 M, 100 mV s−1, all potentials vs. Fc/Fc+. bBroad maximum.
Fig. 4 Cyclic voltammograms of the poly(thiophenes) P4 and P12 (3
scans, MeCN–TBAHFP, 0.1 M, 100 mV s−1).
Fig. 5 Cyclic voltammograms of polythiophene P4 (MeCN–NaClO ,
0.1 M, 100 mV s−1); first scan and each fifth successive scan are shown.
4
and the oligoether thiophenes 13 (DE =−6/−8/12 mV;
pa
Li+/Na+/K+) and 15 (DE =−39/−20/19 mV; Li+/Na+/
pa
Appreciable polymer films were only obtained when the mon-
omer concentration was raised to 0.1 M. Depending on the
number of successive scans polymers are formed whose oxi-
K+), respectively, the peak potential and the shape of the CV
are only slightly affected when an equivalent amount of alkali
metal ions with respect to the monomer concentration is
dation potential is shifted by ca. DE =300 mV to more
positive values in comparison to films polymerized in alkali
metal ion free electrolytes. Despite the electrochemical response
being definitively altered, interestingly, the polymer films pro-
duced in the different electrolytes exhibit nearly the same
pa
added. In contrast, 15-crown-5 thiophene
4
(DE =
pa
99/81/42 mV; Li+/Na+/K+) and 18-crown-6 thiophene 14
(DE =7/159/187 mV; Li+/Na+/K+) exhibit relatively large
pa
positive shifts of the peak potential in the CVs. In the latter
case not only a displacement of the peak is found, but a new
oxidation peak including an isopotential point arises at more
positive potentials upon addition of sodium or potassium ions
(Table 6). This trend is also reflected in the corresponding
polymers P4 and P12. For 15-crown-5 polythiophene P4 the
oxidation peak successively shifts to more positive potentials
and the electroactivity is decreased. After 50 scans, the polymer
absorption maxima (l =607 and 601 nm, respectively). This
finding is in accordance with the results for the other series of
max
polymers and again clearly indicates that under both conditions
polymers with about the same mean conjugation length and
morphology are obtained. Thus, the influence on the electro-
chemical response by complexation of alkali metal ions in the
crown ether moieties is not caused by a reduction of the mean
conjugation length via twisting of the thiophene units, but by
a change of the diffusion behavior of counter ions into the
polymer film. Due to electrostatic interactions with the com-
plexed cations the penetration of counter anions into the film
is rendered more difficult when the polythiophene backbone
is oxidized. Thus, charge compensation occurs at more positive
potentials and the functionalized polymer is more difficult
to oxidize.
exhibited
a selectivity for sodium ions (DE =600 mV)
pa
whereas the effect is minor for lithium (DE =150 mV) and
pa
potassium ions (DE =50 mV) (Fig. 5).4f In good accordance
pa
with the corresponding monomers, the 12-crown-4 polythi-
ophene P12 showed only small effects in the presence of alkali
metal ions. After 50 scans the peak potentials are only
marginally shifted in the corresponding 0.1 M salt solution
(Li+: DE =20 mV; Na+: DE =40 mV; K+: DE =0 mV).
pa
pa
pa
With respect to the selectivity, these experiments show that
the behavior of both the monomers and the polymers is in
agreement with extraction experiments.18
Summary
In order to get more insight into the mechanism, 15-crown-
5 thiophene 4 was polymerized potentiodynamically in an
electrolyte which already contained 0.1 M of sodium ions.
We have described the syntheses, the electrochemical and
optical properties of two series of crown and oligoether-
functionalized poly(bithiophenes) in which several structural
Table 6 Influence of alkali cations on the electrochemical response of monothiophenes 4, 12–15 and poly(bithiophenes) P4, P12
DE /mV
DE /mV
DE /mV
pa
LiClO a
4
pa
pa
KPF a
6
(M),(P)
NaClO a
Influence
4
12 (12-C-4)
4 (15-C-5)
14 (18-C-6)
13 (OE-4)
−6
99
7
−6
−39
20
18
81
159
−8
−20
40
18
42
187
12
19
0
Li+, Na+&K+
Na+, K+&Li+
15 (OE-6)
P12 (12-C-4)
P4 (15-C-5)
150
600
50
Na+&Li+&K+
aConcentration of the monomer/alkali cation is 151.
2146
J. Mater. Chem., 1999, 9, 2139–2150

parameters were varied. We observe that the electrochemical
behavior of polymers P2, P7–P9 in which the crown ether
units are separated from the conjugated backbone via insulat-
ing oxaalkyl spacers and of polymer P4 from the other series
is strongly influenced in the presence of alkali ions. Selectivities
corresponding to the match of the cation size without solvent
shell and the inner diameter of the crown ether units are
found. Supporting optical and spectroelectrochemical experi-
ments on these novel polymers clearly reveal that the changes
in electronic properties are due to a hindered diffusion of the
counter anions into the film which is necessary for charge
compensation when the conjugated polymer is oxidized.
Finally, our investigation gives a detailed insight into the
structural prerequisites necessary for materials which transduce
a host–guest interaction and therefore chemical information
into the change of an electrical signal.
transferred via Teflon tube connected needles to another
apparatus and added dropwise to an ice cooled suspension of
12.3 g (32.2 mmol) 2-bromo-3-(10-bromodecyl)thiophene 19
and 64.0 mg (0.12 mmol, 0.37 mol%) Ni(dppp)Cl in 50 ml
2
diethyl ether. After 37 h under reflux the reaction mixture is
hydrolyzed with 1 M hydrochloric acid and extracted with
diethyl ether. After drying with sodium sulfate the solvent is
evaporated and the resulting oil is distilled twice under reduced
pressure to yield 4.01 g (10.4 mmol, 32%) of a clear yellowish
oil: bp 141–156 °C (5·10−3 Torr). 1H NMR (CDCl ): d (ppm)
3
7.30 (dd, 3J
=5.0 Hz, 4J
=1.3 Hz, 1 H, 5∞-H), 7.17 (d,
(5∞,4∞)
(5∞,3∞)
3J =5.2 Hz, 1 H, 5-H), 7.10 (dd, 3J
=3.6 Hz, 4J
=
(5,4)
(3∞,4∞)
(3∞,5∞)
(a,b)
1.3 Hz, 1 H, 3∞-H), 7.06 (dd, 3J
=5.0 Hz, 3J
=3.6 Hz,
(5∞,4∞)
(4∞,3∞)
1 H, 4∞-H), 6.92 (d, 3J =5.2 Hz, 1 H, 4-H), 3.40 (t, 3J
=
(4,5)
6.9 Hz, 2 H, H ), 2.74 (t, 3J =7.6 Hz, 2 H, H ), 1.90–1.78
a
(i,j)
j
(m, 2 H, H ), 1.68–1.56 (m, 2 H, H ), 1.53–1.27 (m, 12 H, H
to H ). 13C NMR (CDCl ): d (ppm) 139.6 (C-3∞), 136.2 (C-
2◊), 130.5 (C-2∞), 129.8 (C-4∞), 127.3 (C-4◊), 125.9 (C-3◊),
125.2 (C-5◊), 123.7 (C-5∞), 34.0, 32.8, 30.7, 29.4, 29.1, 28.7,
28.1 (C to C ). Anal. calcd. for C H BrS : C 56.09, H 6.54,
S 16.64, Br 20.73. Found: C 56.32, H 6.52, S 16.43, Br 20.75%.
UV (CH Cl ): l (log e)=295 nm (3.97), 248 nm (3.87).
b
i
c
h
3
Experimental
General procedures
a
j
18 25
2
Melting points are not corrected. 1H- and 13C-NMR spectro-
scopic data were obtained with a Bruker ACF 250 or AC 250
2
2
max
instrument with CDCl as solvent using TMS as standard. J
values are given in Hz. All solvents were distilled prior to use.
Diethyl ether was distilled from sodium–benzophenone ketyl,
2-[2-Oxa-12-(2,2∞-bithienyl-3-yl)dodecyl]-1,4,7,10-
tetraoxacyclododecane 7
3
1.10 g (5.33 mmol) 12-Crown-4-methanol are added dropwise
to a suspension of 2.00 g (5.92 mmol) 3-(10-bromodecyl)-2,2∞-
bithiophene 21, 100 mg (0.29 mmol, 5 mol%) TBAHS and
3 ml 50% sodium hydroxide solution in 7 ml benzene. After
68 h at 75 °C the reaction mixture is poured on water, extracted
with dichloromethane and the organic layer washed with
sodium bicarbonate and dried over sodium sulfate. After
evaporation of the solvent the resulting oil is chromatographed
on silica gel with ethyl acetate followed by chromatography
with dichloromethane yielding 1.49 g (2.92 mmol, 55%) of a
acetonitrile from phosphorous pentoxide. DMF was distilled
from CaH under reduced pressure. The following compounds
2
were prepared according to literature procedures: 3-(10-brom-
odecyl)thiophene (17),4a 3-(5-bromopentyl)-2,2∞-bithiophene
(20),4a 2-hydroxymethyl-1,4,7,10-tetraoxacyclododecane (12-
crown-4-methanol),35 2-hydroxymethyl-1,4,7,10,13,16-hexa-
oxacyclooctadecane (18-crown-6-methanol),35 2,5-bis(ethoxy-
carbonyl)-3,4-dihydroxythiophene,18,20,36 2,5,8,11-tetraoxa-
14-thiabicyclo[10.3.0]pentadeca-1(15),12-diene,18 2,5,8,11,14-
pentaoxa-17-thiabicyclo[13.3.0]octadeca-1(18),15-diene,18 2,
5,8,11,14,17-hexaoxa-20-thiabicyclo[16.3.0]heneicosa-1(21),
18-diene,18 ethylene glycol monomethyl ether monotosylate,38
diethylene glycol monomethyl ether monotosylate,37 tetraethy-
lene glycol monomethyl ether.38 All spectroscopic and analyt-
ical data are in agreement with the structures and the data
slightly yellow clear oil. 1H NMR (CDCl ): d (ppm) 7.29 (dd,
3
3J
=5.1 Hz, 4J
=1.2 Hz, 1 H, 5◊ H), 7.16 (d, 3J
=
(5◊,4◊)
(5◊,3◊)
(5∞,4∞)
5.2 Hz, 1 H, 5∞-H), 7.10 (dd, 3J
1 H, 3◊-H), 7.05 (dd, 3J
4∞-H), 6.92 (d, 3J
=3.6 Hz, 4J
=1.2 Hz,
=5.0 Hz, 1 H,
(3◊,4◊)
(3◊,5◊)
=3.6 Hz, 3J
=5.2 Hz, 1 H, 4∞-H), 3.89–3.59 (m, 14
(4◊,3◊)
(4◊,5◊)
(4∞,5∞)
H, 3-H to 12-H), 3.51–3.36 (m, 5 H, H , H , 2-H), 2.74 (t,
reported.
N-Bromosuccinimide
(Fluka),
Ni(dppp)Cl
a
c
2
3J =7.8 Hz, 2 H, H ), 1.65–1.49 (m, 4 H, H , H ), 1.27 (s,
(Aldrich), tetraethylene glycol (Merck), tetrabutylammonium
hydrogen sulfate (TBAHS, Aldrich) were used as received.
(l,k)
l
d
k
12 H, H to H ). 13C NMR (CDCl ): d (ppm) 139.6 (C-3∞),
e
j
3
136.2 (C-2◊), 130.5 (C-2∞), 129.9 (C-4∞), 127.3 (C-4◊), 126.0
(C-3◊), 125.3 (C-5◊), 123.7 (C-5∞), 78.6, 71.8, 70.9, 70.8, 70.7,
70.4, 70.2 (C-2 to C-12, C , C ), 30.7, 29.5, 29.4, 29.1, 26.1
(C to C ). Anal. calcd. for C H O S : C 63.49, H 8.29, S
27 42 5 2
12.56. Found: C 63.36, H 8.40, S 12.62%. UV (CH Cl ): l
max
2-Bromo-3-(10-bromodecyl)thiophene 19
a
c
Under nitrogen atmosphere 13.5 g (75.9 mmol) N-bromo-
succinimide, dissolved in 60 ml DMF, are added to a solution
of 23.0 g (75.8 mmol) 3-(10-bromodecyl)thiophene 17 in 60 ml
DMF and stirred for five hours at ambient temperature. The
reaction mixture is poured on water and extracted with
dichloromethane. The organic phase is washed with saturated
sodium bicarbonate solution and dried over sodium sulfate.
After evaporation of the solvent the resulting oil is distilled
twice but the starting material could not be completely
removed (ca. 7%, GC-analysis). Yield: 12.3 g (32.2 mmol,
42%) of a clear colorless oil; bp 148–153 °C (5·10−3 Torr); 1H
NMR (CDCl ): d (ppm) 7.16 (d, 3J =5.8 Hz, 1 H, 5-H),
d
l
2
2
(log e)=294 nm (3.95), 249 nm (3.84).
19-(2,2∞-Bithienyl-3-yl)-2,5,8,11,14-pentaoxanonadecane 8
1.00 g (4.80 mmol) Tetraethylene glycol monomethyl ether are
added dropwise to a suspension of 1.66 g (5.26 mmol) 3-(5-
bromopentyl)-2,2∞-bithiophene 20, 80.6 mg (0.24 mmol,
4.5 mol%) TBAHS and 2.4 ml 50% aqueous sodium hydroxide
solution in 5 ml benzene. After 30 h at 70 °C the reaction
mixture is poured on water, extracted with dichloromethane
and the organic layer washed with sodium bicarbonate and
dried over sodium sulfate. After evaporation of the solvent
the resulting oil is chromatographed on silica gel with ethyl
acetate–hexane yielding 1.07 g (2.41 mmol, 50%) of a slightly
3
(5,4)
6.77 (d, 3J =5.5 Hz, 1 H, 4-H), 3.39 (t, 3J =6.9 Hz, 2
(4,5) (a,b)
H, H ), 2.54 (t, 3J =7.6 Hz, 2 H, H ), 1.89–1.78 (m, 2 H,
(j,i)
H ), 1.58–1.28 (m, 14 H, H to H ). 13C NMR (CDCl ): d
a
j
b
c
i
3
(ppm) 141.9 (C-3), 128.2 (C-4), 125.1 (C-5), 108.8 (C-2) 34.0,
32.8, 29.7, 29.4, 29.3, 29.1, 28.7, 28.1 (C to C ).
yellow clear oil. 1H NMR (CDCl ): d (ppm) 7.29 (dd, 3J
=
3
(5◊,4◊)
a
j
4.9 Hz, 4J
1 H, 5∞-H), 7.09 (dd, 3J
3◊-H), 7.04 (dd, 3J
6.92 (d, 3J
to 13-H), 3.44 (t, 3J
1-H), 2.75 (t, 3J
=1.2 Hz, 1 H, 5◊-H), 7.16 (d, 3J
=5.2 Hz,
(5◊,3◊)
(5∞,4∞)
=3.7 Hz, 4J
=1.2 Hz, 1 H,
3-(10-Bromodecyl)-2,2∞-bithiophene 21
(3◊,4◊)
(3◊,5◊)
=5.0 Hz, 3J
=5.2 Hz, 1 H, 4∞-H), 3.53–3.66 (m, 16 H, 3-H
=3.5 Hz, 1 H, 4◊-H),
(5◊,4◊)
(4◊,3◊)
Under an inert gas atmosphere 6.55 g (40.2 mmol) 2-bromo-
thiophene in 40 ml dry diethyl ether are added dropwise to
0.98 g (40.2 mmol) magnesium turnings in 10 ml diethyl ether.
After formation of the Grignard reagent this solution is
(4∞,5∞)
=6.4 Hz, 2 H, 15-H), 3.37 (s, 3 H,
(15,14)
=7.6 Hz, 2 H, 19-H), 1.71–1.55 (m, 4
(19,18)
H, 18-H, 16-H), 1.46–1.35 (m, 2 H, 17-H). 13C NMR (CDCl ):
3
J. Mater. Chem., 1999, 9, 2139–2150
2147

d (ppm) 139.3 (C-3∞), 136.1 (C-2◊), 130.5 (C-2∞), 129.8 (C-4∞),
127.3 (C-4◊), 125.9 (C-3◊), 125.2 (C-5◊), 123.7 (C-5∞), 71.9,
71.3, 70.5, 70.4, 70.0 (C-3 to C-15), 59.0 (C-1), 30.5, 29.4,
evaporation of the solvent the resulting oil is chromatographed
twice on aluminium oxide with diethyl ether yielding 1.07 g
(1.61 mmol, 40%) of a green–yellow oil. 1H NMR (CDCl ): d
3
29.0, 25.9 (C-16 to C-19). Anal. calcd. for C H O S : C
(ppm) 7.29 (dd, 3J
=5.1 Hz, 4J
=1.4 Hz, 2 H, 5◊-H),
22 34 5 2
(5◊,4◊)
(5◊,3◊)
59.70, H 7.74, S 14.49. Found: C 59.73, H 7.63, S 14.33%. UV
7.16 (d, 3J
=5.5 Hz, 2 H, 5∞-H), 7.10 (dd, 3J
=3.7 Hz,
=5.1 Hz,
=5.5 Hz, 2 H, 4∞-
(5∞,4∞)
(3◊,4◊)
(CH Cl ): l
(log e)=295 nm (3.96), 248 nm (3.87).
4J
=1.2 Hz,
=3.7 Hz, 2 H, 4◊-H), 6.92 (d, 3J
2
H, 3◊-H), 7.05 (dd, 3J
2
2
max
(3◊,5◊)
(4◊,5◊)
3J
(4◊,3◊)
(4∞,5∞)
H), 3.65–3.52 (m, 16 H, 7-H to 17-H), 3.43 (t, 3J
=
2-[2-Oxa-7-(2,2∞-bithienyl-3-yl)heptyl]-1,4,7,10,13,16-
hexaoxacyclooctadecane 9
(5,4;19,20)
6.6 Hz, 4 H, 5-H, 19-H), 2.75 (t, 3J
=7.8 Hz, 4 H, 1-
(1,2;23,22)
H, 23-H), 1.71–1.55 (m, 8 H, 2-H, 4-H, 20-H, 22-H), 1.46–1.36
0.52 g (1.76 mmol) 18-Crown-6-methanol are added dropwise
to a suspension of 0.64 g (2.03 mmol) 3-(5-bromopentyl)-2,2∞-
bithiophene 20, 34.0 mg (0.1 mmol) TBAHS and 1 ml 50%
aqueous sodium hydroxide solution in 3 ml benzene. After
26 h at 65 °C the reaction mixture is poured on water, extracted
with dichloromethane and the organic layer washed with
sodium bicarbonate and dried over sodium sulfate. After
evaporation of the solvent the resulting oil is chromatographed
on aluminium oxide with dichloromethane–acetone (753)
yielding 0.67 g (1.27 mmol, 72%) of yellow–brown clear oil.
(m, 4 H, 3-H, 21-H). 13C NMR (CDCl ): d (ppm) 139.3 (C-
3∞), 136.1 (C-2◊), 130.5 (C-2∞), 129.8 (C-4∞), 127.3 (C-4◊), 126.0
(C-3◊), 125.3 (C-5◊), 123.7 (C-5∞), 71.3, 70.5, 70.0, 65.8 (C-5
to C-19), 30.5, 29.4, 29.0, 26.0 (C-1 to C-4, C-18 to C-23).
3
Anal. calcd. for C H O S : C 61.60, H 6.99, S 19.35. Found:
34 46 5 2
C 61.40, H 6.98, S 19.15%. UV (CH Cl ): l
(log e)=
2
2
max
295 nm (4.25), 248 nm (4.15).
3,4-Bis(2-methoxyethoxy)-2,5-bis(ethoxycarbonyl)thiophene
23
1H NMR (CDCl ): d (ppm) 7.30 (dd, 3J
=5.0 Hz,
3
(5◊,4◊)
4J
=1.3 Hz, 1 H, 5◊-H), 7.16 (d, 3J
=5.2 Hz, 1 H, 5∞-
Under inert gas atmosphere 20.8 g (79.9 mmol) 2,5-bis(ethoxy-
carbonyl)-3,4-dihydroxythiophene, 40.5 g (176 mmol) ethy-
lene glycol monomethyl ether monotosylate, 12.2 g
(88.3 mmol) potassium carbonate and 50 ml dry DMF are
mixed together and heated for 26 h to 100 °C. The hot solution
is filtered and the solvent evaporated under reduced pressure.
The resulting oil is distilled three times with a Kugelrohr
yielding 26.3 g (69.8 mmol, 87%) of a yellow oil: bp 170–180 °C
(5◊,3◊)
(5∞,4∞)
H), 7.10 (dd, 3J
(dd, 3J
=3.5, 4J
=1.2 Hz, 1 H, 3◊-H), 7.05
(3◊,4◊)
(3◊,5◊)
=5.0 Hz, 3J
=3.6 Hz, 1 H, 4◊-H), 6.92 (d,
(4◊,5◊)
(4◊,3◊)
3J
=5.2 Hz, 1 H, 4∞-H), 3.82–3.39 (m, 27 H, H , H , 1-H
(4∞,5∞)
a
c
to 18-H), 2.74 (t, 3J =7.7 Hz, 2 H, H ), 1.70–1.53 (m, 4 H,
(g,f)
g
H , H ), 1.45–1.33 (m, 2 H, H ). 13C NMR (CDCl ): d (ppm)
f
d
e
3
139.4 (C-3∞), 136.2 (C-2◊), 130.6 (C-2∞), 129.8 (C-4∞), 127.3 (C-
4◊), 126.0 (C-3◊), 125.3 (C-5◊), 123.8 (C-5∞), 78.4, 71.5, 70.9,
70.8, 70.7, 67.0 (C-2 to C-18, C , C ), 26.0, 29.0, 29.5, 30.5
(5·10−3 Torr). 1H NMR (CDCl ): d (ppm) 4.34–4.26 (m, 8 H,
a
c
3
(C to C ). Anal. calcd. for C H O S : C 59.06, H 7.63, S
26 40 7 2
12.13. Found: C 59.00, H 7.75, S 12.22%. UV (CH Cl ): l
max
1∞-H, 3∞-H), 3.70–3.67 (m, 4 H, 2∞-H), 3.37 (s, 6 H, 4∞-H),
d
g
1.33 (t, 3J
=7.2 Hz, 6 H, 4∞-H). 13C NMR (CDCl ): d
2
2
(4◊,3◊)
3
(log e)=295 nm (3.97), 248 nm (3.87).
(ppm) 160.6 (C-1◊), 153.0, 119.9 (C-2 to C-5), 73.5, 71.5, 61.3,
58.9 (C-1∞ to C-4∞, C-3◊), 14.2 (C-4◊). Anal. calcd. for
C H O S: C 51.05, H 6.43, S 8.52. Found: C 50.96, H 6.41,
2-[2-Oxa-12-(2,2∞-bithienyl-3-yl)dodecyl]-1,4,7,10,13,16-
hexaoxacyclooctadecane 10
16 24 8
S 8.66%. UV (CH Cl ): l
(log e)=283 nm (4.15).
2
2
max
1.75 g (5.93 mmol) 18-Crown-6-methanol are added dropwise
to a suspension of 1.82 g (5.39 mmol) 3-(10-bromodecyl)-2,2∞-
bithiophene 21, 100 mg (0.29 mmol) TBAHS and 3 ml 50%
aqueous sodium hydroxide solution in 7 ml benzene. After
43 h at 70 °C the reaction mixture is poured on water, extracted
with dichloromethane and the organic layer washed with
sodium bicarbonate and dried over sodium sulfate. After
evaporation of the solvent the resulting oil is chromatographed
on aluminium oxide with ethyl acetate followed by a second
chromatography on aluminium oxide with diethyl ether yield-
ing 1.72 g (2.88 mmol, 53%) of a slighlty brown clear oil. 1H
3,4-Bis[2-(2-methoxyethoxy)ethoxy]-2,5-bis(ethoxycarbonyl)
thiophene 24
Under an inert gas atmosphere a mixture of 13.1 g (0.05 mol)
2,5-bis(ethoxycarbonyl)-3,4-dihydroxythiophene and 9.88 g
(0.17 mol) potassium fluoride in 350 ml dry acetonitrile is
stirred for one hour at room temperature. The yellow suspen-
sion is heated under reflux and a solution of 30.7 g (0.11 mol)
diethylene glycol monomethyl ether monotosylate in 100 ml
dry acetonitrile is slowly added via a dropping funnel. After
24 h under reflux the solution is filtered and the solvent
evaporated. The resulting brown oil is extracted with chloro-
form. After concentration of the solution the resulting oil is
chromatographed twice on silica gel (first ethyl acetate, second
diethyl ether) yielding 7.11 g (15.3 mmol, 31%) of a yellow oil.
NMR (CDCl ): d (ppm) 7.29 (dd, 3J
=5.0 Hz, 4J
=
3
(5◊,4◊)
(5◊,3◊)
1.3 Hz, 1 H, 5◊-H), 7.16 (d, 3J
=5.2 Hz, 1 H, 5∞-H), 7.10
(5∞,4∞)
(dd, 3J
=3.6 Hz, 4J
=1.3 Hz, 1 H, 3◊-H), 7.06 (dd,
(3◊,4◊)
(3◊,5◊)
3J
=5.0 Hz, 3J
=3.6 Hz, 1 H, 4◊-H), 6.92 (d, 3J
=
(4◊,5◊)
(4◊,3◊)
(4∞,5∞)
5.2 Hz, 1 H, 4∞-H), 3.83–3.39 (m, 27 H, 2-H to 18-H, H , H ),
2.73 (t, 3J =7.8 Hz, 2 H, H ), 1.65–1.52 (m, 4 H, H , H ),
1H NMR (CDCl ). d (ppm) 4.35–4.25 (m, 8 H, 1∞-H, 3◊-H),
a
c
d
3
3.80–3.77 (m, 4 H, 2∞-H), 3.66–3.62 (m, 4 H, 4∞-H), 3.51–3.47
(l,k)
l
k
1.26 (s, 12 H, H to H ). 13C NMR (CDCl ): d (ppm) 139.6
(m, 4 H, 5∞-H), 3.33 (s, 6 H, 7∞-H), 1.33 (t, 3J
=7.2 Hz,
j
e
3
(4◊,3◊)
(C-3∞), 136.2 (C-2◊), 130.5 (C-2∞), 129.9 (C-4∞), 127.3 (C-4◊),
125.9 (C-3◊), 125.3 (C-5◊), 123.7 (C-5∞), 78.4, 71.8, 71.6, 70.9,
70.7, 70.6, 69.9 (C-2 to C-12, C , C ), 30.7, 29.5, 29.1, 26.1
6 H, 4◊-H). 13C NMR (CDCl ): d (ppm) 160.6 (C-1◊), 153.1,
3
119.6 (C-2 to C-5), 73.6, 71.9, 70.5, 70.3, 61.3, 59.0 (C-1∞ to
C-7∞, C-3◊), 14.2 (C-4◊). Anal. calcd. for C H O S: C 51.71,
a
c
20 32 10
(C to C ). Anal. calcd. for C H O S : C 62.17, H 8.42, S
31 50 7 2
10.71. Found: C 62.23, H 8.29, S 10.64%. UV (CH Cl ): l
max
H 6.94, S 6.90. Found: C 51.79, H 7.06, S 6.98%. UV (CH Cl ):
d
l
2 2
l
(log e)=283 nm (4.14).
2
2
max
3,4-Bis(2-methoxyethoxy)thiophene 13
(log e)=294 nm (3.95), 248 nm (3.85).
1,23-Bis(2,2∞-bithienyl-3-yl)-6,9,12,15,18-pentaoxatricosane 11
7.53 g (20.0 mmol) 3,4-Bis(2-methoxyethoxy)-2,5-bis(ethoxy-
carbonyl)thiophene are dissolved in 100 ml ethanol and 100 ml
5% aqueous sodium hydroxide solution are added. The mixture
is heated for two hours at 60 °C. After that time the solution
is acidified under ice cooling with concentrated hydrochloric
acid. The formed solid is filtered off, dried and decarboxylated
under reduced pressure (15 Torr) at 250 °C. The formed black
mixture is extracted with dichloromethane, filtered through
0.78 g (4.02 mmol) Tetraethylene glycol are added dropwise
to a suspension of 3.00 g (9.50 mmol) 3-(5-bromopentyl)-2,2∞-
bithiophene 20, 161 mg (0.48 mmol) TBAHS and 4 ml 50%
aqueous sodium hydroxide solution in 10 ml benzene. After
47 h at 70 °C the reaction mixture is poured on water, extracted
with dichloromethane and the organic layer washed with
sodium bicarbonate and dried over sodium sulfate. After
2148
J. Mater. Chem., 1999, 9, 2139–2150

silica gel and the solvent evaporated. The resulting oil is
distilled twice in a Kugelrohr yielding 1.78 g (7.66 mmol, 38%)
of a clear colorless oil: bp 105 °C (5·10−3 Torr). 1H NMR
References
1
(a) S. J. Higgins, Chem. Soc. Rev., 1997, 26, 247; (b) M. Leclerc
and K. Faid, Adv. Mater., 1997, 9, 1087; (c) T. M. Swager, Acc.
Chem. Res., 1998, 31, 201.
(CDCl ): d (ppm) 6.20 (s, 2 H, 2-H, 5-H), 4.11–4.08 (m, 4 H,
3
1∞-H), 3.73–3.69 (m, 4 H, 2∞-H), 3.39 (s, 6 H, 4∞-H). 13C NMR
2
3
F. Garnier, Angew. Chem. 1989, 101, 529.
(CDCl ): d (ppm) 147.1, 97.9 (C-2 to C-5), 70.7, 69.6, 59.0
(a) M. R. Bryce, A. Chissel, P. Kathirgamanthan, D. Parker and
N. R. M. Smith, J. Chem. Soc., Chem. Commun., 1987, 466; (b)
J. Roncali, R. Garreau and M. Lemaire, J. Electroanal. Chem.,
1990, 278, 373; (c) J. Roncali, L. H. Shi and F. Garnier, J. Phys.
Chem., 1991, 95, 8983; (d) H. S. Li, F. Garnier and J. Roncali,
Synth. Met., 1991, 41–43, 547; (e) L. H. Shi, F. Garnier and
J. Roncali, Solid State Commun., 1991, 77, 811; ( f ) R. D.
McCullough, S. Tristram-Nagle, S. P. Williams, R. D. Lowe and
M. Jayaraman, J. Am. Chem. Soc., 1993, 115, 4910; (g) R. D.
McCullough and S. P. Williams, J. Am. Chem. Soc., 1993, 115,
11608; (h) I. Le´vesque and M. Leclerc, J. Chem. Soc., Chem.
Commun., 1995, 2293; (i) I. Le´vesque and M. Leclerc, Chem.
Mater., 1996, 8, 2843; ( j) I. Le´vesque and M. Leclerc, Synth. Met.,
1997, 84, 203; (k) R. D. McCullough, P. C. Ewbank and R. D.
Lowe, J. Am. Chem. Soc., 1997, 119, 633.
3
(C-1∞ to C-4∞). Anal. calcd. for C H O S: C 51.71, H 6.94, S
10 16 4
13.80. Found: C 51.93, H 7.01, S 13.70%. UV (CH Cl ): l
(log e)=255 nm (3.86).
2
2
max
3,4-Bis[2-(2-methoxyethoxy)ethoxy]thiophene 15
7.11 g (15.3 mmol) 3,4-Bis[2-(2-methoxyethoxy)ethoxy]-2,5-
bis(ethoxycarbonyl)thiophene are dissolved in 80 ml ethanol
and 80 ml 5% aqueous sodium hydroxide solution are added.
After 5 h at 60 °C the solution is cooled with an ice bath and
acidified with concentrated hydrochloric acid. It is then
extracted with diethyl ether and the solvent evaporated under
reduced pressure. The remaining solid is decarboxylated at
210–220 °C for 1.5 h. The resulting black mixture is extracted
with dichloromethane and filtered through silica gel. After
evaporation of the solvent the resulting oil is distilled twice
with a Kugelrohr apparatus yielding 0.90 g (2.79 mmol, 18%)
of a slightly brownish clear oil. Bp 140 °C (5·10−3 Torr). 1H
4
(a) P. Bauerle and S. Scheib, Adv. Mater., 1993, 5, 848; (b)
¨
M. J. Marsella and T. M. Swager, J. Am. Chem. Soc., 1993, 115,
12 214; (c) Y. Miyazaki and T. Yamamoto, Chem. Lett., 1994, 41;
(d) T. M. Swager and M. J. Marsella, Adv. Mater., 1994, 6, 595;
(e) M. J. Marsella, P. J. Carroll and T. M. Swager, J. Am. Chem.
Soc., 1994, 116, 9347; ( f ) P. Bauerle and S. Scheib, Acta Polym.,
¨
1995, 46, 124; (g) M. J. Marsella, P. J. Carroll and T. M. Swager,
J. Am. Chem. Soc., 1995, 117, 9832; (h) T. Benincori, E. Brenna,
F. Sannicolo, L. Trimarco, G. Moro, D. Pitea, T. Pilati, G. Zerbi
and G. Zotti, J. Chem. Soc., Chem. Commun., 1995, 881;
(i) Y. Miyazaki and T. Yamamoto, Synth. Met., 1995, 69, 317; ( j)
T. Yamamoto, M. Omote, Y. Miyazaki, A. Kashiwazaki, B.-
L. Lee, T. Kanbara, K. Osakada, T. Inoue and K. Kubota,
Macromolecules, 1997, 30, 7158.
NMR (CDCl ): d (ppm) 6.17 (s, 2 H, 2-H, 5-H), 4.10 (t,
3
3J
=5.0 Hz, 4 H, 1∞-H), 3.81 (t, 3J
=5.0 Hz, 4 H, 2∞-
(1∞,2∞)
(2∞,1∞)
H), 3.68–3.64 (m, 4 H, 4∞-H), 3.53–3.49 (m, 4 H, 5∞-H), 3.34
(s, 6 H, 7∞-H). 13C NMR (CDCl ): d (ppm) 147.0, 97.8 (C-2
to C-5), 71.8, 70.6, 69.7, 69.4, 58.9 (C-1∞ to C-7∞). Anal. calcd.
3
for C H O S: C 52.48, H 7.55, S 10.01. Found: C 52.14, H
14 24 6
5
6
G. Rimmel and P. Bauerle, Synth. Met., in the press.
¨
7.56, S 10.08%. UV (CH Cl ): l
(log e)=255 nm (3.88).
(a) P. N. Bartlett, A. C. Benniston, L.-Y. Chung, D. M. Dawson
and P. Moore, Electrochim. Acta, 1991, 36, 1377; (b) H. K.
Youssoufi, M. Hmyene, F. Garnier and D. Delabouglise, J. Chem.
Soc., Chem. Commun., 1993, 1550; (c) H. K. Youssoufi, A. Yassar,
S. Baiteche, M. Hmyene and F. Garnier, Synth. Met., 1994, 67,
251; (d) H. K. Youssoufi, M. Hmyene, A. Yassar and F. Garnier,
J. Electroanal. Chem., 1996, 406, 187.
2
2
max
Electrochemical methods
Tetrabutylammonium hexafluorophosphate, lithium perchlor-
ate, sodium perchlorate and potassium hexafluorophosphate
were recrystallized and dried in vacuo prior to use. Acetonitrile
(Chromasolv, Merck) was filtered through activated basic
alumina and saturated with oxygen-free argon. All electro-
chemical measurements were performed with a computer-
controlled EG&G PAR 273 potentiostat or a computer-con-
trolled EG&G PAR363 potentiostat. The platinum working
electrode was a platinum wire sealed in a soft glass tube with
a surface of A=0.785 mm2 and polished down to 0.5 mm
(Buehler polishing paste) prior to use in order to get reproduc-
ible surfaces. The counter electrode consisted of a platinum
wire, the reference was an Ag/AgCl secondary electrode.
General procedure for the electrosynthesis of polythiophenes:
acetonitrile–tetrabutylammonium hexafluorophosphate (0.1
M) was deoxygenated with dry argon for 15 min. The corre-
sponding monomers were characterized at a concentration of
1.10−3 mol l−1. Then the concentration was increased to the
given values and the monomers were electropolymerized by
successive scanning in the given potential range. The modified
working electrodes were subsequently rinsed with dry aceto-
nitrile, dried in air, and characterized in electrolyte free of
monomer.
7
8
9
(a) M. J. Marsella, R. J. Newland, P. J. Carroll and T. M. Swager,
J. Am. Chem. Soc., 1995, 117, 9842; (b) K. B. Crawford, M. B.
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10 (a) A. Emge and P. Bauerle, Synth. Met., 1997, 84, 213; (b)
¨
P. Bauerle and A. Emge, Adv. Mater., 1998, 9, 324.
¨
11 (a) T. Livache, A. Roget, E. Dejean, C. Barthet, G. Bidan and
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12 A. Meyer and P. Bauerle, unpublished results.
¨
13 E. K. Wilson, Chem. Eng. News, 1998, May 25, 47.
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¨
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¨
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Paper 9/02823D
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J. Mater. Chem., 1999, 9, 2139–2150