Structure-reactivity relationships in bithiophenic precursors based on the 3-phenoxythiophene building block

Article abstract of DOI:10.1039/b502164b

3-Toluoxythiophene and bithiophenes diversely substituted by toluoxy groups have been synthesized. Theoretical, spectroscopic and electrochemical studies show that the number and position of the phenoxy groups exert a strong influence on the geometry of t

Full text of DOI:10.1039/b502164b

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Structure–reactivity relationships in bithiophenic precursors based on the
3-phenoxythiophene building block
Philippe Leriche,* Pierre Fre`re and Jean Roncali*
Received 11th February 2005, Accepted 1st July 2005
First published as an Advance Article on the web 25th July 2005
DOI: 10.1039/b502164b
3-Toluoxythiophene and bithiophenes diversely substituted by toluoxy groups have been synthesized.
Theoretical, spectroscopic and electrochemical studies show that the number and position of the
phenoxy groups exert a strong influence on the geometry of the ground state and cation radical and
determine the reactivity of the latter and hence its aptitude for electropolymerization.
3-Toluoxythiophene has already been described by Hellberg
Introduction
et al. in a short conference paper, in which it was reported
as poorly reactive.13 Consequently, we have also synthesized
Organic materials derived from thiophene-based linear
p-conjugated systems are intensively investigated as electrode
materials1 or organic semi-conductors for the realization of
position of the phenoxy groups has been varied, and we report
bithiophenes 2, 3 and 4 (Scheme 1) in which the number and
devices such as field effect transistors,2 light-emitting diodes3
here a comparative analysis of their reactivity using cyclic
and solar cells.4
voltammetry and theoretical calculations.
The development of these various fields creates a continuous
demand for the synthesis of new functional p-conjugated
Results and discussion
structures with tailored chemical, optical or electrical pro-
perties. This situation, in turn, generates a need for new
synthetic routes, new methods of functionalization and new
building blocks.
3-toluoxythiophene
1 was obtained by condensation of
p-cresol and 3-bromothiophene in the presence of copper
and potassium carbonate.14 Bromination of 1 with one
equivalent of NBS in DMF at 0 uC gave selectively 3-(p-
tolyloxy)-2-bromothiophene 5 in 77% yield. Treatment of 1
with two equivalents of bromine in a boiling mixture of
chloroform and acetic acid gave the dibromo compound 6 in
70% yield. Treatment of 6 with one equivalent of butyllithium
at low temperature followed by hydrolysis gave 80% of a 1 : 1
mixture of the 2-bromo and 5-bromo (7) compounds which
were separated by chromatography. Oxidative coupling of 1 by
successive addition of n-BuLi and CuCl2 led to bithiophene 3
isolated in 10% yield after recrystallisation in petroleum ether.
A Stille coupling of 2-tributylstannylthiophene with com-
pound 5 led to the monosubstituted bithiophene 2 in 65%
yield. A symmetrical coupling of the in situ generated stannyl
derivative of compound 7 in the presence of Pd0 (Pd(OAc)2)
and CuCl2 gave bithiophene 4 in 20% yield. All new
compounds were satisfactorily characterized by NMR and
mass spectrometry.
Among the large number of substituents which have been
used for the derivatization of polythiophene (PT),5 the phenyl
group appears particularly interesting as it represents an
interesting platform for further functionalization.6–12 Polythio-
phenes based on monomer containing phenyl groups have
been investigated at an early stage of the development of this
class of polymers.6 In 1990 we described a series of PTs
containing substituted phenyl rings, electronically and steri-
cally disconnected from the conjugated system.7
In an attempt to develop new analogues of 3,4-ethyl-
enedioxythiophene(EDOT) which could be substituted at sp2
carbons we have recently synthesized 3,4-phenylenedioxythio-
phene (PheDOT) and the corresponding polymers.12 However,
experimental and theoretical results have shown that because
of the delocalization of the HOMO over the whole molecule,
the introduction of the phenyl ring to form a dioxin-like
structure results in a strong stabilization and hence loss of
reactivity of the corresponding cation radical.12
In a continuation of these investigations we now report the
synthesis of precursors of polythiophenes derivatized by
phenoxy groups. In addition to the release of the steric
constraint associated with the direct connection of a phenyl
ring at the 3-position of thiophene, such compounds are
expected to contribute to a better understanding of the
electronic effects associated with the introduction of phenoxy
substituents on the electronic properties and reactivity of
the thiophene ring.
X-Ray diffraction{
The crystallographic structure of compound 3 has been
analyzed on a single crystal. This derivative crystallizes in
{ Orange prism (0.62 6 0.33 6 0.19 mm3), C11H9O1S1, Mr 5 189.24,
˚
˚
orthorhombic, space group Pbcn, a 5 19.056(2) A, b 5 7.536(1) A, c 5
13.524(1) A, V 5 1942.1(4) A , Z 5 8, T 5 293 K, rcalc 5 1.294 g cm23
,
3
˚
˚
m (Mo Ka) 5 0.287 mm21, F(000) 5 792, hmin 5 2.91u, hmax 5 25.81u,
10599 reflections collected, 1859 unique (Rint 5 0.0741), restraints/
parameters 5 0/154, R1 5 0.0461 and wR2 5 0.1163 using 1139
reflections with I . 2s(I), R1 5 0.0776 and wR2 5 0.1290 using all
data, GOF 5 0.971, 20.185, dr , 0.297 e A23. CCDC reference
˚
Groupe Syste`mes Conjugue´s Line´aires, CIMMA, UMR 6200 CNRS,
Universite´ d’Angers, 2, Bd Lavoisier, F-49045, Angers.
E-mail: jean.roncali@univ-angers.fr
number 263331. See http://dx.doi.org/10.1039/b502164b for crystal-
lographic data in CIF or other electronic format.
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Scheme 1
the orthorhombic Pbcn space group and the formula of the
structure corresponds to half a molecule. As shown in Fig. 1,
the bithiophene system adopts a fully planar geometry with the
two thiophene units in an anti conformation. The non-bonded
˚
S–O distances (y2.90 A), are considerably shorter than the
˚
sum of the van der Waals radii of sulfur and oxygen (3.35 A),
thus confirming the occurrence of non-covalent S–O intra-
molecular interactions which stabilize the planar conforma-
tion of bithiophene, as observed for many EDOT-based
p-conjugated systems.15 Due to steric interactions between
periplanar hydrogens, the phenyl rings are not coplanar with
the bithiophene system and form a dihedral angle of 65u with
the latter.
UV–visible spectroscopy
Fig. 2 shows the UV–vis absorption spectra of compounds 2–4
in methylene chloride. The spectrum of compound 4 shows a
broad structureless absorption band consistent with a high
degree of rotational freedom around the inter-ring single bond.
The spectrum of compound 2 exhibits a discernible vibronic
fine structure with shoulders around 300 and 330 nm which
suggest a more rigid structure due to intramolecular S–O
interactions. This trend becomes more apparent in the
spectrum of compound 3 which shows a better resolved
fine structure as expected for stronger S–O interactions.
Fig. 1 ORTEP view of bithiophene 3
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Fig. 2 UV–vis absorption spectra in CH2Cl2. Long dashed: 4, short
dashed: 2, solid line: 3.
Fig. 3 Top: potentiodynamic electropolymerization of 4, 0.05 M in
0.1 M Bu4NPF6/CH2Cl2 scan rate 100 mV s21. Bottom: CV of poly(4)
Compound 4 shows the most red shifted lmax at 323 nm
suggesting a more delocalized p-electron system than for
compounds 2 and 3 which have practically the same lmax at
311 and 312 nm.
in 0.10 M Bu4NPF6/CH3CN, scan rate 100 mV s21
.
The CV of the resulting polymer recorded in a monomer-
free electrolytic medium exhibits a broad redox system with a
main anodic peak at 0.70 V followed by a shoulder around
1.00 V. The ca. 300 mV negative shift of the potential of the
main anodic peak compared to poly(bithiophene)5 reflects the
electron-releasing effect of the phenoxy group. The polymer
film shows a good stability and no change in electroactivity
(as expressed by the amount of charge reversibly exchanged)
was observed after 100 cycles at 100 mV s21 in either
acetonitrile or water.
Electrochemistry
The electrochemical properties of compounds 1–4 have been
analyzed by cyclic voltammetry in acetonitrile using Bu4NPF6
as electrolyte. The anodic peak potentials (Epa) corresponding
to oxidation to the corresponding cation radicals are listed in
Table 1. As expected bithiophenes 2–4 have Epa values lower
than compound 1, and compounds 3 and 4 with two phenoxy
substituents show less positive Epa values than the mono-
substituted bithiophene 2. The data in Table 1 also show that
compound 3, with phenoxy groups at the inner b-positions
of the bithiophene structure, presents a lower Epa value than
compound 4.
Note that these results agree well with the observations of
previous works of Heinze and coworkers on oligothiophenes
substituted by methoxy and methylsulfanyl groups.16–18
Theoretical studies
Electro-oxidation of compound 1 leads to the appearance
of a blue coloration on the anode surface but no polymer
deposition occurs. A similar behaviour is observed for com-
pounds 2 and 3 although the latter compound presents the
lowest oxidation potential of the series.
In order to elucidate the behaviour of the oxidized species,
we have undertaken theoretical calculations. Ab initio quantum
calculations have been performed on compounds 1–4 with the
Gaussian 9819 package of programs at a hybrid density
functional theory20 (DFT) level. Calculations have been done
using the restricted B3LYP/6-31G* function for neutral states
and at the U-B3LYP/6-31G* level for the cation radical
states.21,22
Application of repetitive potential scans to a 0.05 M
solution of compound 4 in methylene chloride leads to a
typical potentiodynamic electropolymerization curve with the
progressive development of a broad redox system correspond-
ing to the doping/undoping process of the growing polymer in
the 0.50 to 1.00 V region (Fig. 3).
HOMO, LUMO levels of neutral molecules 1, 3 and 4 are
collected in Table 1. Although compound 4 presents a torsion
of 32.5u between the thiophene cycles, the move of the phenoxy
groups from outer to inner position leads to a planarization of
the conjugated systems for derivative 3 which shows a dihedral
angle of only 4.8u. In addition to the X-ray structure for the
solid state and UV–vis spectroscopy for the diluted solution,
calculations for the gas phase show again the key role of the
oxygen atoms at the inner position for stabilizing the planar
Table 1 Calculated HOMO and LUMO energy level and anodic
peak potentialsb for compounds 1, 3 and 4a
Epa/V
HOMO/eV
LUMO/eV
1
2
3
4
a
1.83
1.22
1.02
1.19
25.78
—
25.26
25.65
20.37
—
21.10
21.42
…
conformation of bithiophenic system by S O intramolecular
Calculated on 3-phenoxythiophene instead of 3-toluoxythiophene.
Ref Ag.AgCl, in 0.10 M Bu4NPF6/CH2Cl2.
interactions. Consequently, the HOMO level of derivative 3 is
higher than the one of 4. These results are well correlated with
b
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theoretical calculations show that the number and position of
the phenoxy groups exert a strong influence on the reactivity of
the cation radical. Thus, whereas the introduction of phenoxy
groups at the inner b-positions of the bithiophene structure
suppresses the aptitude of the cation radical to polymerize,
their grafting at the outer b-positions of bithiophene has the
reverse effect by increasing the SOMO coefficient at the 2,59
coupling positions, in agreement with experimental results.
Experimental
1H NMR and 13C NMR spectra were recorded on a Bruker
AVANCE DRX 500 spectrometer operating at 500.13 and
125.7 MHz; d are given in ppm (relative to TMS) and coupling
constants (J) in Hz. Mass spectra were recorded under EI or
FAB mode on a VG-Autospec mass spectrometer, under
MALDI-TOF mode on a MALDI-TOF-MS BIFLEX III
Bruker Daltonics spectrometer or under positive electrospray
(ESI) on a JMS-700 JEOL mass spectrometer of reversed
geometry. UV–visible optical data were recorded with a
PerkinElmer lambda 19 spectrophotometer. IR spectra were
recorded on a PerkinElmer model 841 spectrophotometer,
samples being embedded in KBr discs or thin films between
NaCl plates. Melting points were obtained from a Reichert-
Jung Thermovar hot-stage microscope apparatus and are
uncorrected. Column chromatography purifications were
carried out on Merck silica gel Si 60 (40–63 mm).
Scheme 2
the electrochemical properties which show that compound 3 is
easier to oxidize.
The oxidation to radical cation is accompanied by structural
change. For both compounds, the cation radical adopts a
planar geometry with the largest SOMO coefficients located on
the carbons of the bithiophene system forming the pathway
linking the two oxygen atoms. The analysis of the geometries
of radical cations shows that for the two radical cations,
as expected for a pseudo-quinoid structure, the central C–C
bond is shortened. On the other hand, the C–O bonds lengths
linking thiophene cycles with phenoxy groups are also
shortened indicating a localization of the positive charge on
an oxygen atom. Such structures are consistent with an
important contribution of the mesomeric forms A and B
(Scheme 2) for radical cations 3 and 4. The cation radical of
compound 3 possess a maximum density of unpaired electrons
on the internal part of the molecule which does not favour the
coupling reaction. On the contrary, the outer localization of
toluoxy groups of 4+ allows delocalization of unpaired
electrons on the whole bithiophene skeleton, including the
terminal position which favours polymerization.
Electrochemical experiments were performed with a EG&G
273 potentiostat in a standard three-electrode cell using an
Ag/AgCl reference electrode. The solutions were degassed by
argon bubbling and experiments were carried under an argon
blanket. The working electrode was a 1 mm Pt disk sealed
in glass. Tetrabutylammonium hexafluorophosphate (Fluka
puriss) was used as received.
3-(p-Tolyloxy)2-bromothiophene 5
3-(p-tolyloxy)thiophene (1) (1 g, 5.3 mmol) was dissolved in
20 mL of dry DMF under a nitrogen atmosphere at 0 uC, in
the dark. Then, one equivalent of freshly recrystallized NBS
dissolved in 20 mL of DMF was added dropwise. After 2 h
stirring at 0 uC, and 2 h at room temperature, 150 mL of water
was added and the mixture was extracted with diethyl ether.
The organic phase was washed with water and dried over
MgSO4. After evaporation of the solvent, purification by
column chromatography (silica gel, petroleum ether) gave 77%
1
Conclusion
of compound 5 as a colorless oil. H NMR (CDCl3): 7.23 (d,
1H, 3J 5 5.88); 7.11 (d, 2H, 3J 5 8.54); 6.87 (d, 2H, 3J 5 8.54);
To summarize, 3-toluoxythiophene and three bithiophenes
diversely substituted by toluoxy groups have been synthesized.
The crystal structure of one of the bithiophenes reveals short
non-bonded sulfur-oxygen distances indicating that the intra-
molecular non-covalent interactions, already observed in many
conjugated systems containing 3,4-ethylenedioxythiophene15
or methoxythiophene units23, also occur in some 3-phenoxy-
thiophene-based compounds.
3
6.66 (d, 1H, J 5 5.87); 2.32 (3H). 13C NMR (CDCl3): 155.3;
151.3; 132.6; 130.1; 124.8; 121.0; 116.7; 97.7; 20.6.
3-(p-Tolyloxy)-2,5-dibromothiophene 6
3-(p-Tolyloxy)thiophene (1) (0.5 g, 2.6 mmol) was dissolved in
a mixture of 30 mL of chloroform and 30 mL of acetic acid.
Then, 2.2 equivalent of bromine dissolved in chloroform was
added dropwise and the mixture was refluxed overnight. The
mixture was poured into 300 mL of ethyl acetate, the organic
phase was washed with water and aqueous NaHCO3 to
neutrality and dried on MgSO4. After evaporation of the
Ab initio quantum calculations performed with a hybrid
density functional theory have shown that the introduction of
phenoxy groups markedly affects the geometry of the ground
state and the energy level of the frontier orbitals. Futhermore,
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solvent column chromatography (SiO2, petroleum ether) gave
70% of compound 5 as a colorless oil. 1H NMR (CDCl3): 7.12
(d, 2H, 3J 5 8.37); 6.89 (s, 1H); 6.88 (d, 2H, 3J 5 8.37); 6.66 (s,
1H); 2.33 (s, 3H), together with 10% of 3-(4-(bromomethyl)-
phenoxy)-2,5-dibromothiophene as a white solid, 78 uC, 1H
stirred for 30 min at this temperature and 1.5 equivalent of
tributylstannyl chloride was added. The brown–red solution
immediately turned orange. After return to room temperature
and removal of the solvent, the residue was dissolved in 15 mL
of ethyl acetate and stirred for 45 min with 20 mL of a
saturated aqueous solution of sodium fluoride. After flash
filtration onto celite, the organic phase was washed with water
and dried on MgSO4. After evaporation of the solvent, the
crude stannic derivative was dissolved in dry THF and two
equivalent of CuCl2 and a catalytic amount of Pd(OAc)2 (5%
mol.) were added. The mixture was stirred overnight under
nitrogen at room temperature. After filtration on celite and
evaporation of the solvent, column chromatograpy (silica gel,
petroleum ether) gave 30 mg (20%) of the target compound as
a light yellow solid, mp y 100 uC(dec) 1H NMR (CDCl3): 7.15
(d, 4H, 3J 5 8.55); 7.15 (d, 4H, 3J 5 8.45); 6.92 (d, 2H,
3
NMR (CDCl3) 7.35 (d, 2H, J 5 8.64); 6.89 (s, 1H); 6.93 (d,
3
2H, J 5 8.64); 6.72 (s, 1H); 4.49 (s, 2H), mp 78 uC
4-(pTolyloxy)-2-bromothiophene 7
Dibromo compound 6 (0.6 g, 1.7 mmol) was dissolved in 30 mL
of dry diethyl ether under a nitrogen atmosphere and cooled
to 278 uC. After addition of one equivalent of n-BuLi the
mixture was stirred for 1 h at 278 uC. After addition of a
mixture of water/methanol and a return to room temperature,
the organic phase was washed with water and dried on MgSO4.
After evaporation of the solvent and chromatography (silica
gel, petroleum ether) the target compound was isolated in 40%
4
4J 5 1.49); 6.41 (d, 2H, J 5 1.44); 2.34 (s, 6H). MS (TOF):
1
M+ 378.8 (cal 378.07).
yield together with 40% of 3-(p-tolyloxy)bromothiophene. H
NMR (CDCl3): 7.14 (d, 2H, 3J 5 8.33); 6.95 (d, 2H, 3J 5 8.47);
6.83 (d, 1H, 4J 5 1.84); 6.40 (d, 1H, 4J 5 1.78); 2.34 (s, 3H).13C
NMR (CDCl3): 154.8; 154.0; 133.4; 130.2; 123.3; 118.3; 111.8;
106.9; 20.7.
Acknowledgements
The authors thank Dr Jacques Delaunay for NMR and mass
spectrometry analyses and Magali Allain for crystallographic
analyses.
3-(p-Tolyloxy)-2-(thiophen-2-yl)thiophene 2
Compound 5 (0.6 g, 2.2 mmol) was dissolved in dry toluene
and the solution was carefully degassed with dry nitrogen.
After addition of 2-tributylstannylthiophene (1.2 g,1.5 eq)
and 30 mg of freshly recristallized Pd(PPh3)4, the mixture
was refluxed overnight under a nitrogen atmosphere. After
evaporation of the solvent, the residue was dissolved in 50 mL
of ethyl acetate and stirred for 30 min with 50 mL of saturated
sodium fluoride. The organic phase was washed with water
and dried on MgSO4. After removal of the solvent, column
chromatography (SiO2, petroleum ether) gave 65% of the
References
1 J. Roncali, J. Mater. Chem., 1999, 9, 1875.
2 C. D. Dimitrakopolous and P. Malenfant, Adv. Mater., 2002, 14,
99.
3 U. Mitschke and P. Ba¨uerle, J. Mater. Chem., 2000, 10, 1471.
4 C. J. Brabec, N. S. Sariciftci and J. C. Hummelen, Adv. Funct.
Mater., 2001, 11, 15.
5 J. Roncali, Chem. Rev., 1992, 92, 711.
6 K. Kaeriyama, M. Sato and S. Tanaka, Synth. Met., 1987, 18, 223.
7 J. Roncali, H. Korri-Youssoufi, R. Garreau, M. Lemaire and
F. Garnier, J. Chem. Soc., Chem. Commun., 1990, 414.
8 D. J. Guerero, X. Ren and J. P. Ferraris, Chem. Mater., 1994, 6,
1437.
9 H. Sarker, Y. Gofer, J. C. Lillian, T. O. Poehler and P. C. Searson,
Synth. Met., 1998, 97, 1.
¨
10 Q. Pei, H. Ja¨rvinen, J. E. Osterholm, O. Ingana¨s and J. Laakso,
1
target compound as a colourless oil. H NMR (CDCl3) 7.26
(d*d, 1H, 3J 5 3.48, 4J 5 0.96); 7.19 (d*d, 1H, 3J 5 5.11,
4J 5 0.96); 7.11 (d, 2H, 3J 5 8.55); 7.09 (d, 1H, 3J 5 5.69); 6.99
(d, 1H, 3J 5 5.1, 3J 5 3.6); 6.93 (d, 2H, 3J 5 8.55); 6.72 (d, 2H,
3J 5 5.48); 2.34 (s, 3H). MS (TOF): M+ 271.8 (cal. 272.03).
Macromolecules, 1992, 25, 4297.
11 G. E. Collins, A. K. Burrell, S. M. Scott and D. L. Officer, J. Org.
Chem., 2003, 68, 8974.
3-(p-Tolyloxy)-2-(3-(p-tolyloxy)thiophen-2-yl)thiophene 3
12 S. Roquet, P. Leriche, I. Perepichka, B. Jousselme, E. Levillain,
P. Fre`re and J. Roncali, J. Mater Chem., 2004, 14, 1393.
13 J. Hellberg, T. Remonen, M. Johansson, O. Ingana¨s, M. Theander,
L. Engman and P. Eriksson, Synth. Met., 1997, 84, 251.
14 J. W. H. Watthey and M. Desai, J. Org. Chem., 1982, 47, 1755.
15 (a) J. Roncali, P. Blanchard and P. Fre`re, J. Mater Chem., 2005,
15, 1589; (b) M. Turbiez, P. Fre`re, P. Blanchard and J. Roncali,
Tetrahedron Lett., 2000, 41, 5521; (c) J.-M. Raimundo,
P. Blanchard, P. Fre`re, N. Mercier, I. Ledoux-Rak, R. Hierle
and J. Roncali, Tetrahedron Lett., 2001, 42, 1507; (d) J. J. Aperloo,
L. Groenendaal, H. Verheyen, M. Jayakannan, R. A. J. Janssen,
A. Dkhissi, D. Beljonne, R. Lazzaroni and J.-L. Bre´das, Chem.
Eur. J., 2002, 8, 2384; (e) M. Turbiez, P. Fre`re and J. Roncali,
J. Org. Chem., 2003, 68, 5367; (f) P. Leriche, M. Turbiez,
V. Monroche, P. Fre`re, P. Blanchard, P. J. Skabara and
J. Roncali, Tetrahedron Lett., 2003, 44, 469; (g) M. Turbiez,
P. Fre`re, M. Allain, C. Videlot, J. Ackermann and J. Roncali,
Chem. Eur. J., 2005, 11, 3742.
Compound 1 (0.5 g, 2.6 mmol) was dissolved in 30 mL of
dry diethyl ether under a nitrogen atmosphere and cooled to
278 uC. After addition of one equivalent of n-BuLi the
mixture was stirred for 1 h at 78u and copper chloride
(1.2 equivalent) was added in one portion. After stirring
overnight at room temperature, the mixture was washed with
water and dried on MgSO4. After evaporation of the solvent,
the residue was recrystallised in petroleum ether to give
compound 4 in 10% yield, mp 150 uC. 1H NMR (CDCl3): 7.11
3
4
(m, 3H); 6.93 (d, 2H, J 5 8.50); 6.71 (d, 1H, J 5 5.55); 2.32
(s, 3H). M S (TOF): M+ 377.9 (cal 378.07).
4-(p-tolyloxy)-2-(4-(p-tolyloxy)thiophen-2-yl)thiophene 4
16 J. Heinze and M. Dietrich, Synth. Met., 1991, 41–43, 503.
17 P. Tschuncky and J. Heinze, Synth. Met., 1993, 55, 1603.
18 A. Smie, A. Synowczyk, J. Heinze, R. Alle, P. Tschunck, G. Go¨tz
and P. Ba¨uerle, J. Electroanal. Chem., 1998, 452, 87.
4-(p-Tolyloxy)-2-bromothiophene 7 (0.2 g 0.74 mmol) was
dissolved in 30 mL of dry diethyl ether at 278 uC. After
dropwise addition of 1.1 equivalent of n-BuLi the mixture was
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View Article Online
19 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, V. G. Zakrzewski,
J. A. Montgomery, Jr., R. E. Stratmann, J. C. Burant,
S. Dapprich, J. M. Millam, A. D. Daniels, K. N. Kudin,
M. C. Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi,
R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford,
J. Ochterski, G. A. Petersson, P. Y. Ayala, Q. Cui, K. Morokuma,
D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman,
J. Cioslowski, J. V. Ortiz, A. G. Baboul, B. B. Stefanov, G. Liu,
A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts,
R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng,
A. Nanayakkara, C. Gonzalez, M. Challacombe, P. M. W. Gill,
B. G. Johnson, W. Chen, M. W. Wong, J. L. Andres, M. Head-
Gordon, E. S. Replogle and J. A. Pople, GAUSSIAN 98
(Revision A.9), Gaussian, Inc., Pittsburgh, PA, 1998.
20 A. D. Becke, Phys. Rev. A, 1988, 38, 3098; A. D. Becke, J.Chem.
Phys., 1993, 98, 5648.
21 C. Lee, W. Yang and R. G. Parr, Phys. Rev. B, 1988, 37, 785.
22 (a) P. Flu¨kiger, H. P. Lu¨thi, S. Portmann and J. Weber, Molekel,
Version 4.2, Swiss Center for Scientific Computing, Manno
(Switzerland), 2000, http://www.cscs.ch/molekel/; (b) S. Portmann
and H. P. Lu¨thi, Chimia, 2000, 54, 766.
23 M. Turbiez, P. Fre`re, P. Leriche, N. Mercier and J. Roncali, Chem.
Commun., 2005, 1161.
3478 | J. Mater. Chem., 2005, 15, 3473–3478
This journal is ß The Royal Society of Chemistry 2005