Regiospecifically alkylated oligothiophenes via structurally defined building blocks

Article abstract of DOI:10.1055/s-2002-32543

We have developed a new synthetic protocol for the unsymmetrically alkylated and halogenated terthiophenes 5 and 10. To demonstrate their usefulness as building blocks for well-defined oligothiophenes, we synthesized a series of seven new sexi-, septi- and octithiophenes. Terthiophene 5 could be dimerized to the didecylsexithiophene In6 and terthiophene 10 to sexithiophene Out6, respectively, by the use of nickel catalysis. Together with the bisstannylated thiophenes 11 and 12, the septithiophenes In7 and Out7 as well as the octithiophenes In8 and Out8 could be obtained via Stille coupling methodology. We could also obtain the unsymmetrical sexithiophene Unsym6 by selective heterocoupling between one equivalent of terthiophene 5 and 10 each. All new sexi, septi- and octithiophenes show high photoluminescence in solution, but the quantum yield drops sharply in thin films of the materials.

Full text of DOI:10.1055/s-2002-32543

PAPER
1195
Regiospecifically Alkylated Oligothiophenes via Structurally Defined Building
Blocks
R
egiospecifica
r
lly
A
lky
e
lated Oligo
d
thiophenes
v
r
ia Struc
t
i
urally D
k
efined Building
Bv
locks on Kieseritzky,a Jonas Hellberg,*a Xiangjun Wang,b Olle Inganäsb
a
Department of Chemistry, Organic Chemistry, Royal Institute of Technology, 100 44 Stockholm, Sweden
Fax +46(879)12333; E-mail: jhel@kth.se
b
Biomolecular and Organic Electronics, Department of Physics and Measurement Technology, Linköping University, 581 83 Linköping,
Sweden
Received 25 April 2002
bility of different regioisomers, both in oligomers and
polymers. While 3-alkylated thiophene monomers have
been successfully polymerized regioselectively,4 there is a
lack of synthetic procedures that generate regioselectively
Abstract: We have developed a new synthetic protocol for the un-
symmetrically alkylated and halogenated terthiophenes 5 and 10.
To demonstrate their usefulness as building blocks for well-defined
oligothiophenes, we synthesized a series of seven new sexi-, septi-
and octithiophenes. Terthiophene 5 could be dimerized to the dide- alkylated oligomers, both for use as such, and for further
cylsexithiophene In6 and terthiophene 10 to sexithiophene Out6,
respectively, by the use of nickel catalysis. Together with the bis-
stannylated thiophenes 11 and 12, the septithiophenes In7 and Out7
functionalization–polymerization.
Since the stability of a light-emitting diode depends on the
number of coupling defects in the constituting polymer
(among other things),5 it should be of interest to synthe-
size well-defined longer oligomers. Furthermore, as the
diode efficiency is a function of several structural param-
eters, it should also be worthwhile to investigate different
regioselectively alkylated oligomers, where different
alkyl ‘dilutions’ of the -system are possible. In addition
to creating different conjugation lengths, different propor-
tions of sp3-chains should also affect solubility, which
previously has been proposed as a way of optimizing the
photoluminescence yield.6
as well as the octithiophenes In8 and Out8 could be obtained via
Stille coupling methodology. We could also obtain the unsymmet-
rical sexithiophene Unsym6 by selective heterocoupling between
one equivalent of terthiophene 5 and 10 each. All new sexi-, septi-
and octithiophenes show high photoluminescence in solution, but
the quantum yield drops sharply in thin films of the materials.
Key words: regioselectivity, halogenation, alkylations, coupling,
oligothiophenes, luminescence
Oligomers and polymers of substituted thiophenes have
received considerable attention in the last years owing to
potential applications of both scientific and economic val-
ue.1 Alkyl substitution enhances molecular systems’ solu-
bilities, thereby enabling the creation of applications that
demand processability. The alkyl substitution can also al-
ter the conjugation length of the thiophene chain by caus-
ing the thiophene units to assume separate planes from
each other.2
Terthiophenes can be considered key building blocks for
oligothiophenes. We therefore anticipated that it should
be valuable to develop synthetic routes to terthiophenes,
with regioselective alkyl and halogen substitution, there-
by facilitating further regioselective oligomerization–
functionalization. We chose the unsymmetrically substi-
tuted terthiophenes 5 and 10 as useful, and until now, un-
known targets for synthesis. We also chose a decyl group
as the alkyl chain for our systems, since we thought it
would be of sufficient length to solubilize the higher oli-
gomers, and because starting materials are easily avail-
able.
The main application for oligo- and polythiophenes has
traditionally been the electroactive component in light-
emitting diodes (LEDs) and field-effect transistors
(FETs). Thiophenes synthesized for FET-applications are
typically substituted in the free peripheral -positions,3
whereas LED-thiophenes have substituents in the -posi-
tions.2 The latter substitution pattern opens up the possi-
Previous syntheses of terthiophenes have usually consist-
ed of organometallic coupling of two thiophene subunits
to one central substituted unit,7 or ring-closure of disubsti-
Scheme 1 Reactions and conditions: i) Bromine, NBS or other brominating reagent
Synthesis 2002, No. 9, Print: 01 07 2002.
Art Id.1437-210X,E;2002,0,09,1195,1200,ftx,en;C12302SS.pdf.
© Georg Thieme Verlag Stuttgart · New York
ISSN 0039-7881

1196
F. von Kieseritzky et al.
PAPER
tuted 1,3-diacetylene8 or 1,4-butadione segments9 by dif-
ferent thionating reagents. None of these methods have
been successful for the synthesis of -alkylsubstituted ter-
thiophenes with regioselective halogen attachment. Re-
ported brominations of unsymmetrically alkylsubstituted
terthiophenes have not been selective (Scheme 1).10
We therefore anticipated that a useful synthesis must in-
clude a halogenated building block, which is assembled to
the desired terthiophene without scrambling. Our synthe-
sis is depicted in Scheme 2. 2-Bromothiophene (1) was
acylated with n-dodecanoyl chloride in quantitative yield
to give 2, which conveniently and quantitatively could be
brominated to the ketone, with elemental bromine to
give compound 3. We adopted the method of Kelin and
Kulinkovich11 to transform 3 and 2-acetylthiophene to the
corresponding unsymmetrically substituted 1,4-dithie-
nylbutandione 4 in moderate yield (63%). The ring-clo-
sure of 4 to the corresponding thiophene proved a more
demanding task than first expected. The common reagents
for this transformation, like phosphorus pentasulfide or
Lawesson’s reagent, gave high yields of debrominated,
reduced terthiophene, despite claims in the literature that
these reagents are inert toward aryl bromides.12 We are
not sure if this debromination occurs before the cycliza-
tion, or whether it is the thionating reagent or one of its re-
action products that is the active species in this undesired
side-reaction. Noteworthy is however that reduction of the
target terthiophenes (5 or 10) does not occur with either
phosphorus pentasulfide or Lawesson’s reagent under
similar conditions. In addition, we could somewhat sup-
press reduction by using very large excess of thionating
reagent, leading to the assumption that the reduction is
caused by one of the reaction products from the phosphor-
us reagent.
Scheme 2 Reactions and conditions: i) n-Dodecanoyl chloride, alu-
minium chloride; ii) bromine; iii) diethylamino magnesium bromide,
2-acetylthiophene; iv) hexamethyldisilathiane, boron trichloride; v)
diethylaminomagnesium bromide, 5-bromo-2-acetylthiophene
The desired non-reductive cyclization could, on the other
hand, conveniently be carried out by the phosphorus-free
procedure of Freeman et al. and Steliou et al.,13 where
hexamethyldisilathiane is reacted with a 1,4-butanedione
in the presence of boron trichloride (in situ creating bo-
rontrisulfide as the thionating reagent). This reaction af-
forded the target terthiophene 5 in 51% yield of excellent
purity. Analogously, the second target terthiophene 10
could be synthesized from thiophene (6).
Once we had created these valuable building blocks, we
could proceed to synthesize a series of regio-defined olig-
othiophenes (Figure 1). Since the systematic names of
these oligomers are rather inconvenient, we decided to
give them more graphic acronyms than what is usual. The
position of the alkyl chain is always at the second periph-
eral thiophene unit. Thus the position of the alkyl chain
can be viewed as being either ‘In’ or ‘Out’ depending on
its position on the thiophene. Accordingly, the word ‘In’
or ‘Out’ is followed by the number of thiophene units,
making an acronym like In6 for the first oligothiophene in
the series.
Figure 1 Series of regio-defined oligothiophenes
2,2 -bipyridine.14 It is interesting to note that zinc had to
be added after the addition of the substrate 5 in order to get
the reaction to proceed. Analogously the other regioiso-
meric sexithiophene Out6 could be obtained by dimeriza-
tion of terthiophene 10.
Next, we were able to transform 5 to its corresponding tri-
methylstannyl derivative, and react it with 10 in a one-pot
palladium-catalyzed procedure to yield the unsymmetri-
We synthesized the didecyl-substituted sexithiophene In6
via a nickel-catalyzed dimerization of 5 in the presence of
Synthesis 2002, No. 9, 1195–1200 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Regiospecifically Alkylated Oligothiophenes via Structurally Defined Building Blocks
1197
cally substituted sexithiophene Unsym6, with a very un- els. The photoluminescence efficiencies in solution are a
usual substitution pattern.
few percent higher for the ‘Out’-isomers, compared to the
corresponding ‘In’-isomers, meaning that the alkyl chain
in the ‘Out’-isomers is more effective in hindering the in-
terchain luminescence quenching. The photolumines-
cence efficiencies in films are only a few percent for all
oligomers, which clearly shows that there is not enough
‘sp3-dilution’ of the -system to prevent the interchain lu-
minescence quenching in the solid state. The octimers In8
and Out8 are rather insoluble in chloroform, which clear-
ly limits the measurements.
In order to obtain longer oligomers, we chose the tin-
based Stille procedure, since the central bis-stannylated
bridging units 11 and 12 (Figure 2) are easily obtainable.15
Terthiophene 5 and thiophene 11 conveniently gave sep-
tithiophene In7. Analogously 10 and 11 could be assem-
bled to give Out7. Additionally, bithiophene 12 could be
reacted with terthiophene 5 to yield In8 and in a similar
procedure with 10 to give Out8. We found this Stille
methodology most useful as attempted syntheses of the
same targets, employing boron-based procedures (such as We have developed an efficient synthesis of two new ver-
Suzuki coupling) gave inconsistent and unsatisfactory re- satile building blocks, terthiophenes 5 and 10. With these
sults.
as starting materials, we have synthesized a series of new
and hitherto unavailable sexi- septi- and octithiophenes in
high purity, useful on a preparative scale. All oligomers
show high photoluminescence in solution, whereas inter-
chain quenching drastically reduces the photolumines-
cence efficiency in the solid state. Further synthetic
applications of building blocks 5 and 10 are now pursued
in our laboratory and will be reported in due course.
Figure 2 Bis-stannylated building blocks
All oligothiophenes were collected in 60–90% yield with
these procedures. We could not distinguish any reliable
trends in yields with respect to oligomer lengths or substi-
tution patterns. However, we did observe that one crucial
factor for high yields was the freshness of the stannylated
building blocks. Although no deterioration of compounds
11 and 12 was detectable by NMR, oligomer yields were
consistently higher when using freshly prepared material.
The title compounds, terthiophenes 5 and 10, could on the
other hand be stored at ambient temperature and atmo-
sphere for several months without any detectable degrada-
tion or loss of reactivity.
All operations except where indicated were performed in ambient
atmosphere, without any special care taken for the exclusion of air
or moisture. 1H NMR and 13C NMR spectra were recorded at 400
and 100 MHz, respectively, on a Bruker AM 400. 13C NMR spectra
could not be collected for the sexi-, septi- or octithiophenes, even at
prolonged experiment times (18 h), due to their relatively low solu-
bility in CDCl3, or any other deuterated solvent. Mass spectra were
recorded on a Finnegan SSQ 7000 (electron impact) and on a Per-
septive Biosystems Voyager-De STR (MALDI-TOF). Elemental
analyses were performed by Analytische Laboratorien GmbH, Ger-
many. THF was freshly distilled from sodium benzophenone ketyl,
and DMF was distilled from P2O5 and stored over molecular sieves.
All other commercial reagents and solvents were used as received.
In the optical measurements, the oligomer was dissolved in CHCl3
with concentrations adjusted to give an optical density 0.2 or lower
in a 10 mm optical glass cell. Thin films were spin-coated from
CHCl3 solution, 5–10 mg/mL, on a 24 40 mm2 quartz substrate
giving optical densities of 0.1–0.3. The optical absorption spectra of
samples were measured on a Perkin Elmer 9 spectrometer, and the
emission spectra were measured with an Oriel Instaspec IV diode
matrix spectrometer. Photoluminescence (PL) yields and spectra
were measured in a custom built integrating sphere made by Lab-
We investigated the optical properties of the new oligo-
mers (Table) and found that all ‘Out’-oligomers show a
small bathochromic shift compared to their ‘In’-isomers.
All oligomers display high luminescence in chloroform
solution, as expected for soluble thiophene oligomers.
The emission wavelengths were identical for all oligo-
mers of the same length, showing that the position of the
alkyl group does not alter the emissive state’s energy lev-
Table Optical Properties of Oligothiophenes
Absorption Maxima (nm)
Emission Maxima (nm)
PL Quantum Efficiency (%)
Compound
In6
Solution
415
Film
Solution
515, 555
515, 555
515, 555
530, 570
530, 570
545, 585
545, 585
Film
Solution
24
Film
3.7
1.9
2.3
3.5
2.2
4.7
˜
445, 473, 613
425, 501
445, 473, 512
457, 482, 523
438
580, 630
Out6
Unsym6
In7
427
580, 630
31
422
580, 630
28
434
625, 670, 710
625, 710
29
Out7
In8
444
33
444
476, 508, 554
447
625, 675, 710
625, 675, 710
22
Out8
451
25
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F. von Kieseritzky et al.
PAPER
sphere, together with Oriel Instapec IV diode matrix spectrometer.
Exciting light was a chromatic beam and the beam wavelength was
selected according to absorption spectra of each sample.
13C NMR (CDCl3): = 14.5, 23.1, 27.8, 29.7, 29.8, 29.9, 29.9, 30.0,
32.3, 33.4, 41.9, 43.1, 123.2, 128.6, 131.8, 132.6, 132.7, 134.3,
144.0, 146.1, 191.6, 195.4
1-(5-Bromothien-2-yl)-dodecan-1-one (2)
5-Bromo-3 -decyl-[2,2 ;5 ,2 ]terthiophene (5)
2-Bromothiophene (1) (8.16 g, 50 mmol) and n-dodecanoyl chlo-
ride (13.67 g, 62.5 mmol) were dissolved in benzene (75 mL). AlCl3
(8.33 g, 62.5 mmol) was added in portions, with stirring, over 10
min. The resulting black solution was refluxed for 30 min and left
to cool to r.t.. The reaction was quenched by very cautious (exces-
sive frothing!) addition of aq HCl (2 M; 75 mL), affording a yellow
slurry that was rinsed into a separating funnel with benzene (50 mL)
and aq HCl (2 M; 50 mL). The mixture was gently shaken and the
phases separated. The organic phase was washed with aq HCl (2 M;
The 1,4-butadione 4 (7.04 g, 15 mmol) was dissolved in toluene
(150 mL) and hexamethyldisilathiane (5.34 g, 30 mmol) was added
in one portion at r.t., directly followed by BCl3 (1 M in hexanes;
22.5 mL). After 1 h, TLC (EtOAc–heptane, 9:1) indicated total con-
sumption of the starting material, and H2O (100 mL) was added.
The organic phase was separated, washed with a further amount of
H2O (2 150 mL), dried (MgSO4) and evaporated to a dark crude
product that was purified by flash chromatography (heptane) (Rf
0.4). This afforded 5 of excellent purity,
2
75 mL), aq NaOH (2 M; 2 75 mL) and H2O (2 75 mL) and
Yield: 3.55 g (51%); yellowish crystalline product.
passed through a silica column (3 cm diameter, 8 cm long), fol-
lowed by CH2Cl2 (100 mL). Evaporation of the solvent gave pure 2.
1H NMR (CDCl3): = 0.88 (t, J = 6.4 Hz, 3 H), 1.22–1.39 (m, 14
H), 1.63 (q, J = 7.6 Hz, 2 H), 2.68 (t, J = 7.6 Hz, 2 H), 6.86 (d,
J = 3.6 Hz, 1 H), 6.99 (s, 1 H), 7.00–7.02 (m, 2 H), 7.15 (dd,
J = 3.6, 1.2 Hz, 1 H), 7.22 (dd, J = 4.8, 1.2 Hz, 1 H).
13C NMR (CDCl3): = 14.9, 23.5, 30.0, 30.1, 30.2, 30.3, 30.3, 30.4,
31.4, 32.7, 112.5, 124.6, 125.4, 126.9, 127.2, 128.6, 129.3, 131.0,
136.5, 137.8, 138.2, 141.7.
Yield: 17.27 g (quantitative); white solid.
1H NMR (CDCl3): = 0.88 (t, J = 6.4 Hz, 3 H), 1.22–1.40 (m, 16
H), 1.71 (q, J = 7.2 Hz, 2 H), 2.80 (t, J = 7.2 Hz, 2 H), 7.08 (d,
J = 4.0 Hz, 1 H), 7.43 (d, J = 4.0 Hz, 1 H).
13C NMR (CDCl3): = 14.5, 23.1, 25.1, 29.6, 29.7, 29.8, 29.8, 30.0,
32.3, 39.2, 122.6, 131.5, 132.1, 146.4, 192.8.
MS (EI): m/z = 468, 466 (M+, 100).
Anal. Calcd for C22H27BrS3: C, 56.51; H, 5.82. Found: C, 56.37; H,
5.97.
2-Bromo-1-(5-bromothien-2-yl)-dodecan-1-one (3)
The ketone 2 (17.27 g, 50 mmol) was dissolved in CH2Cl2 (300
mL). With stirring, Br2 (8.15 g, 51 mmol) was added dropwise. The
solution was refluxed for 45 min and left to cool to r.t. The dark so-
lution was washed with sat. aq Na2S2O3 (100 mL) and H2O (100
mL), and the organic phase was directly passed through a silica col-
umn (3 cm diameter, 10 cm long), followed by CH2Cl2 (150 mL).
Evaporation of the solvent left pure 3.
1-Thien-2-yldodecan-1-one (7)16
Using the procedure for the synthesis of 2, with thiophene (6) sub-
stituted for 1, the desired product was obtained.
Yield: quantitative; yellow oil.
1H NMR (CDCl3): = 0.88 (t, J = 6.8 Hz, 3 H), 1.21–1.39 (m, 16
H), 1.70–1.78 (m, 2 H), 2.89 (t, J = 7.6 Hz, 2 H), 7.12 (dd, J = 4.8,
J = 4 Hz, 1 H), 7.61 (d, J = 4.8 Hz, 1 H), 7.70 (d, J = 4 Hz, 1 H).
13C NMR (CDCl3): = 14.6, 23.1, 25.2, 29.4, 29.7, 29.7, 29.8, 29.9,
30.0, 32.3, 39.9, 128.4, 132.0, 133.7, 145.0, 194.0.
Yield: 21.21 g (quantitative); yellow oil.
1H NMR (CDCl3): = 0.87 (t, J = 6.8 Hz, 3 H), 1.21–1.40 (m, 16
H), 2.01–2.22 (m, 2 H), 4.86 (t, J = 6.8 Hz, 1 H), 7.13 (d, J = 4.0 Hz,
1 H), 7.56 (d, J = 4.0 Hz, 1 H).
13C NMR (CDCl3): = 14.5, 23.1, 27.8, 29.4, 29.6, 29.7, 29.8, 29.9,
32.3, 34.1, 48.0, 124.4, 131.8, 133.5, 143.1, 186.0.
2-Bromo-1-thien-2-yldodecan-1-one (8)
Using the procedure for the synthesis of 3, with the ketone 7 substi-
tuted for 2, the desired product was obtained.
1-(5-Bromothien-2-yl)-2-decyl-4-thien-2-ylbutane-1,4-dione (4)
To a solution of commercial MeMgBr (3 M in Et2O; 25 mL) in tol-
uene (150 mL), was added diethylamine (4.39 g, 60 mmol) in one
portion. The reaction was stirred at r.t. for 15 min, with apparent re-
lease of methane. The solution was cooled to 0 °C and a separate so-
lution of bromo ketone 3 (21.21 g, 50 mmol) and 2-acetylthiophene
(6.31 g, 50 mmol) in toluene (a few mL), was added over 5 min. The
resulting solution was stirred at 0 °C for 3 h, and the organic phase
was subsequently gently shaken with aq H2SO4 (5% v/v; 100 mL)
and washed with H2O (100 mL). To the clear, orange organic phase,
Et3N (5.06 g, 50 mmol) was added, and the reaction was left at r.t.
to proceed overnight. The organic phase was washed with aq HCl
(2 M; 2 100 mL) and H2O (2 100 mL), dried (MgSO4) and evap-
orated to a dark oil (24.5 g). This crude product was purified by
flash chromatography (3 cm diameter, 15 cm long silica column;
heptane–EtOAc, 9:1) (Rf 0.3). On evaporation, the pooled desired
fractions afforded 4.
Yield: quantitative; orange oil.
1H NMR (CDCl3): = 0.88 (t, J = 6.8 Hz, 3 H), 1.20–1.43 (m, 16
H), 2.04–2.25 (m, 2 H), 4.96 (t, J = 6.8 Hz, 1 H), 7.16 (dd, J = 4.8,
4.0 Hz, 1 H), 7.70 (d, J = 4.8 Hz, 1 H), 7.83 (d, J = 4.0 Hz, 1 H).
13C NMR (CDCl3): = 14.5, 23.1, 27.9, 29.5, 29.7, 29.8, 29.9, 30.0,
32.3, 34.3, 48.8, 128.7, 133.3, 135.3, 141.8, 187.2.
4-(5-Bromothien-2-yl)-2-decyl-1-thien-2-ylbutane-1,4-dione (9)
Using the procedure for the synthesis of 4, with -bromo ketone 8
substituted for 3 and with commercial 5-bromo-2-acetythiophene
instead of 2-acetylthiophene (more toluene was required to make a
solution of these two reagents, compared to the synthesis of com-
pound 4), the desired product was obtained.
Yield: 47%; orange oil.
1H NMR (CDCl3): = 0.87 (t, J = 7.2 Hz, 3 H), 1.17–1.33 (m, 16
H), 1.53–1.62 (m, 1 H), 1.75–1.84 (m, 1 H), 3.00 (dd, J = 17.2, 4.4
Hz, 1 H), 3.50 (dd, J = 17.2, 9.2 Hz, 1 H), 3.85–3.92 (m, 1 H), 7.07
(d, J = 4.0 Hz, 1 H), 7.14 (dd, J = 4.8, 4.0 Hz, 1 H), 7.49 (d, J = 4
Hz, 1 H), 7.63 (dd, J = 4.8, 1.0 Hz, 1 H), 7.82 (dd, J = 4.0, 1.0 Hz,
1 H).
13C NMR (CDCl3): = 14.5, 23.1, 27.7, 29.7, 29.8, 30.0, 30.0, 32.3,
33.5, 41.0, 43.7, 123.2, 128.6, 131.7, 132.6, 132.8, 134.3, 144.5,
145.7, 190.8, 196.0.
Yield: 14.88 g (63%); orange oil.
1H NMR (CDCl3): = 0.87 (t, J = 6.8 Hz, 3 H), 1.17–1.34 (m, 16
H), 1.54–1.63 (m, 1 H), 1.74–1.84 (m, 1 H), 3.09 (dd, J = 17.6 Hz,
J = 4.4 Hz, 1 H), 3.56 (dd, J = 17.6, 9.2 Hz, 1 H), 3.78–3.85 (m, 1
H), 7.11–7.14 (m, 2 H), 7.59 (d, J = 4 Hz, 1 H), 7.63 (dd, J = 5.2,
1.2 Hz, 1 H), 7.75 (dd, J = 4, 1.2 Hz, 1 H).
Synthesis 2002, No. 9, 1195–1200 ISSN 0039-7881 © Thieme Stuttgart · New York

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Regiospecifically Alkylated Oligothiophenes via Structurally Defined Building Blocks
1199
5-Bromo-4 -Decyl-[2,2 ;5 ,2 ]terthiophene (10)
Using the procedure for the synthesis of 5, with the 1,4-dione 9 sub-
stituted for 4, the desired product was obtained in slightly dimin-
ished yield (38%), as a yellow material, that required several days
to crystallize.
1H NMR (CDCl3): = 0.88 (t, J = 6.8 Hz, 3 H), 1.20–1.39 (m, 14
H), 1.64 (q, 2 H, J = 7.6 Hz), 2.71 (t, J = 7.6 Hz, 2 H), 6.89 (d, J = 4
Hz, 1 H), 6.94 (s, 1 H), 6.96 (d, J = 4 Hz, 1 H), 7.06 (dd, J = 5.2, 3.6
Hz, 1 H), 7.12 (dd, J = 3.6, 1.0 Hz, 1 H), 7.31 (dd, J = 5.2, 1.0 Hz,
1 H).
MS (EI): m/z = 774 (M+, 100).
Anal. Calcd for C44H54S6: C, 68.16; H, 7.02. Found: C, 68.02; H,
7.18
3 ,3 -Didecyl-[2,2 ;5 ,2 ;5 ,2 ;5 ,2 ;5 ,2 ]sexithiophene
(Unsym6)
A mixture of terthiophene 5 (467 mg, 1 mmol), hexamethylditin
(656 mg, 2 mmol), and Pd(PPh3)4 (29 mg, 0.025 mmol) in anhyd
THF (5 mL) was heated to reflux under argon for 6 h. To the in situ
formed arylstannane was added terthiophene 10 (467 mg, 1 mmol)
in anhyd THF (5 mL), followed by a second portion of Pd(PPh3)4
(58 mg, 0.050 mmol). After another 18 h of reflux, the solvent was
evaporated, leaving a dark semi-solid. This crude product was puri-
fied according to the general purification procedure.
1H NMR (CDCl3): = 0.88 (m, 6 H), 1.20–1.43 (m, 28 H), 1.62–
1.72 (m, 4 H), 2.71–2.79 (m, 4 H), 7.00–7.05 (m, 4 H), 7.06–7.09
(m, 3 H), 7.11–7.14 (m, 2 H), 7.17 (d, J = 3.6 Hz, 1 H), 7.22 (d,
J = 5.2 Hz, 1 H), 7.32 (d, J = 5.2 Hz, 1 H).
13C NMR (CDCl3): = 14.6, 23.1, 29.7, 29.8, 29.9, 30.0, 30.0, 30.1,
31.0, 32.4, 111.3, 124.0, 126.0, 126.5, 127.2, 127.9, 130.5, 131.1,
134.5, 136.1, 139.2, 140.8.
MS (EI): m/z = 468, 466 (M+, 100).
Anal. Calcd for C22H27BrS3: C, 56.51; H, 5.82. Found: C, 56.40; H,
5.91.
Purification of the Sexi-, Septi- and Octithiophenes; General
Procedure
MS (MALDI-TOF): m/z = 774 (M+, 100).
After evaporation of the solvent, the crude product was treated with
boiling Et2O (ca. 10 mL) and then rapidly cooled down to 0 ºC by
immersing the flask in an ice bath, whereupon the oligothiophene
precipitated as flakes. Cold MeOH (a few mL) was added and the
solids were collected by vacuum-filtration and washed with a little
cold MeOH and acetone. The solids were then adsorbed on ~0.5 g
silica gel and put on top of a dry silica column (1 cm diameter, 5 cm
high). The column was then flushed with hexanes (50 mL) (to re-
move non-polar byproducts), pumped dry, flushed with MeOH (50
mL) (to remove polar byproducts) and again pumped dry. The de-
sired oligomer was then eluted with CH2Cl2 (sexi- and sep-
tithiophenes) or THF (octithiophenes) and the analytically pure
product was collected upon evaporation of the solvent, typically in
60–90% yield, in the form of a brick red amorphous solid.
Anal. Calcd for C44H54S6: C, 68.16; H, 7.02. Found: C, 68.32; H,
6.89.
4 ,3 -Didecyl-[2,2 ;5 ,2 ;5 ,2 ;5 ,2 ;5 ,2 ;5 ,2 ]sep-
tithiophene (In7)
To a dry 25 mL 3-necked round-bottom flask, terthiophene 5 (234
mg, 0.5 mmol), 2,5-bistributylstannylthiophene (11) (166 mg, 0.25
mmol) and Pd(PPh3)4 (58 mg, 0.05 mmol) were added. The system
was flushed with argon for a few min, anhyd DMF (5 mL) was add-
ed and the solution stirred at 80 °C overnight. The product was pre-
cipitated by addition of cold MeOH (50 mL), collected by vacuum-
filtration and then purified according to the general purification pro-
cedure.
1H NMR (CDCl3): = 0.88 (t, J = 6.8 Hz, 6 H), 1.21–1.43 (m, 28
H), 1.68 (q, J = 7.6 Hz, 4 H), 2.77 (t, J = 7.6 Hz, 4 H), 7.00–7.05 (m,
6 H), 7.10 (s, 2 H), 7.13 (d, J = 4.0 Hz, 2 H), 7.17 (d, J = 3.6 Hz, 2
H), 7.22 (d, J = 4.8 Hz, 2 H).
4 ,3 -Didecyl-[2,2 ;5 ,2 ;5 ,2 ;5 ,2 ;5 ,2 ]sexithiophene
(In6)
To a dry 25 mL 3-necked round-bottom flask, anhyd NiCl2 (13 mg,
0.1 mmol), PPh3 (131 mg, 0.5 mmol) and 2,2 -bipyridine (16 mg,
0.1 mmol) were added. The system was flushed with argon for a few
min, dry DMF (1 mL) was added and the solution stirred at 70 °C
for 1 h. A solution of terthiophene 5 (234 mg, 0.5 mmol) in anhyd
THF (2.5 mL) was added in one portion, 3 min later followed by Zn
(82 mg, 1.25 mmol, 300 mesh). (Note: No reaction took place if the
zinc was added before the terthiophene!) The mixture was stirred at
70 °C overnight, diluted with CH2Cl2 (50 mL) and vacuum-filtered
through Celite. The clear organic phase was washed with H2O
(3 50 mL) water, dried (MgSO4) and evaporated. The crude prod-
uct was purified according to the general purification procedure.
MS (MALDI-TOF): m/z = 856 (M+, 100).
Anal. Calcd for C48H56S7: C, 67.24; H, 6.58. Found: C, 67.05; H,
6.54.
3 ,4 -Didecyl-[2,2 ;5 ,2 ;5 ,2 ;5 ,2 ;5 ,2 ;5 ,2 ]sep-
tithiophene (Out7)
The procedure for synthesis of In7, 16, with terthiophene 10 substi-
tuted for 5, afforded the desired product.
1H NMR (CDCl3): = 0.88 (t, J = 6.8 Hz, 6 H), 1.21–1.43 (m, 28
H), 1.66 (q, J = 7.6 Hz, 4 H), 2.73 (t, J = 7.6 Hz, 4 H), 7.02 (s, 2 H),
7.05–7.09 (m, 8 H), 7.13 (d, J = 3.6 Hz, 2 H), 7.32 (d, J = 5.2 Hz, 2
H).
1H NMR (CDCl3): = 0.88 (t, J = 6.8 Hz, 6 H), 1.21–1.43 (m, 28
H), 1.68 (q, J = 7.6 Hz, 4 H), 2.77 (t, J = 7.6 Hz, 4 H), 7.00–7.05 (m,
6 H), 7.13 (d, J = 4.0 Hz, 2 H), 7.17 (d, J = 3.6 Hz, 2 H), 7.22 (d,
J = 4.8 Hz, 2 H).
MS (MALDI-TOF): m/z = 856 (M+, 100).
Anal. Calcd for C48H56S7: C, 67.24; H, 6.58. Found: C, 66.78; H,
6.42
Anal. Calcd for C44H54S6: C, 68.16; H, 7.02. Found: C, 68.28; H,
7.08.
MS (EI): m/z = 774 (M+, 100).
4 ,3 -Didecyl-
[2,2 ;5 ,2 ;5 ,2 ;5 ,2 ;5 ,2 ;5 ,2 ;5 ,2
phene (In8)
The procedure for synthesis of In7, 16, with 5,5 -bistributylstan-
nyl[2,2 ]bithiophene (12) substituted for the bis-stannylated
thiophene 11, afforded the desired product.
1H NMR (CDCl3): = 0.88 (t, J = 6.8 Hz, 6 H), 1.21–1.43 (m, 28
H), 1.68 (q, J = 7.6 Hz, 4 H), 2.77 (t, J = 7.6 Hz, 4 H), 7.00–7.05 (m,
6 H), 7.10 (s, 4 H), 7.13 (d, J = 4.0 Hz, 2 H), 7.17 (d, J = 3.6 Hz, 2
H), 7.22 (d, J = 4.8 Hz, 2 H).
]octithio-
3 ,4 -Didecyl-[2,2 ;5 ,2 ;5 ,2 ;5 ,2 ;5 ,2 ]sexithiophene
(Out6)
The procedure for synthesis of In6, 13, with terthiophene 10 substi-
tuted for 5, afforded the desired product.
1H NMR (CDCl3): = 0.88 (t, J = 6.8 Hz, 6 H), 1.21–1.43 (m, 28
H), 1.66 (q, J = 7.6 Hz, 4 H), 2.73 (t, J = 7.6 Hz, 4 H), 7.02 (s, 2 H),
7.05–7.09 (m, 6 H), 7.13 (d, J = 3.6 Hz, 2 H), 7.32 (d, J = 5.2 Hz, 2
H).
MS (MALDI-TOF): m/z = 938 (M+, 100).
Synthesis 2002, No. 9, 1195–1200 ISSN 0039-7881 © Thieme Stuttgart · New York

1200
F. von Kieseritzky et al.
PAPER
Anal. Calcd for C52H58S8: C, 66.47; H, 6.22. Found: C, 66.25; H,
6.11.
4910. (f) McCullough, R. D.; Williams, S. P. J. Am. Chem.
Soc. 1993, 115, 11608. (g) McCullough, R. D.; Jayaraman,
M. J. Chem. Soc., Chem. Commun. 1995, 135. (h) Chen, T.-
A.; Rieke, R. D. J. Am. Chem. Soc. 1992, 114, 10087.
(i) Chen, T.-A.; Rieke, R. D. J. Am. Chem. Soc. 1995, 117,
233. (j) Wu, X.; Chen, T.-A.; Rieke, R. D. Macromolecules
1995, 28, 2101. (k) Bouman, M. M.; Meijer, E. W. Adv.
Mater. 1995, 7, 385. (l) Loewe, R. S.; Ewbank, P. C.; Liu, J.;
Zhai, L.; McCullough, R. D. Macromolecules 2001, 34,
4324.
3 ,4 -Didecyl-
[2,2 ;5 ,2 ;5 ,2 ;5 ,2 ;5 ,2 ;5 ,2 ;5 ,2
phene (Out8)
]octithio-
The procedure for the synthesis of In7, 16, with 5,5 -bistributylstan-
nyl[2,2 ]bithiophene (12) substituted for the bis-stannylated
thiophene 11 and tertiophene 10 substituted for 5, afforded the de-
sired product.
(5) Johansson, D. M.; Theander, Y. M.; Srdanov, G.; Yu, G.;
Inganäs, O.; Andersson, M. R. Macromolecules 2001, 34,
3716.
(6) Theander, Y. M.; Svensson, M.; Ruseckas, A.; Zigmantas,
D.; Sundström, V.; Andersson, M. R.; Inganäs, O. Chem.
Phys. Lett. 2001, 337, 277.
1H NMR (CDCl3): = 0.88 (t, J = 6.8 Hz, 6 H), 1.21–1.43 (m, 28
H), 1.66 (q, J = 7.6 Hz, 4 H), 2.73 (t, J = 7.6 Hz, 4 H), 7.02 (s, 2 H),
7.05–7.09 (m, 10 H), 7.13 (d, J = 3.6 Hz, 2 H), 7.32 (d, J = 5.2 Hz,
2 H).
MS (MALDI-TOF): m/z = 938 (M+, 100).
(7) For example, see: (a) Gronowitz, S.; Peters, D. Heterocycles
1990, 30, 645. (b) Charloner, P. A.; Gunatunga, S. R.;
Hitchcock, P. B. J. Chem. Soc., Perkin Trans. 2 1997, 8,
1597. (c) Rossi, R.; Carpita, A.; Ciofalo, M.; Houben, J. L.
Gazz. Chim. Ital. 1990, 120, 793.
(8) For example, see: (a) Beny, J.-P.; Dhawan, S. M.; Kagan, J.;
Sundlass, S. J. Org. Chem. 1982, 47, 2201. (b) Perrine, D.
M.; Kagan, J. Heterocycles 1986, 24, 365.
(9) For example, see: (a) Merz, A.; Ellinger, F. Synthesis 1991,
462. (b) Wynberg, H.; Metselaar, J. Synth. Commun. 1984,
14, 1. (c) Kagan, J.; Arora, S. K. Heterocycles 1983, 20,
1941.
(10) For example, see: (a) Eachern, A. M.; Soucy, C.; Leitch, L.
C.; Arnason, J. T.; Morand, P. Tetrahedron 1988, 44, 2403.
(b) Nakayama, J.; Konishi, T.; Murabayashi, S.; Hoshino,
M. Heterocycles 1987, 26, 1793. (c) Effenberger, F.; Grube,
G. Synthesis 1998, 1372. (d) Jones, C. L.; Higgins, S. J. J.
Mater. Chem. 1999, 4, 865. (e) Bäuerle, P.; Pfau, F.;
Schlupp, H.; Würthner, F.; Gaudl, K.-U.; Caro, M. B.;
Fisher, P. J. Chem. Soc., Perkin Trans. 2 1993, 3, 489.
(11) Kelin, A. V.; Kulinkovich, O. G. Synthesis 1996, 330.
(12) Encyclopedia of Reagents for Organic Synthesis, Vol 1;
Wiley: New York, 1995, 530–533; and references cited
therein.
(13) (a) Freeman, F.; Kim Darrick, S. H. L.; Rodriguez, E. J. Org.
Chem. 1992, 57, 1722. (b) Steliou, K.; Mrani, M. J. Am.
Chem. Soc. 1982, 104, 3104.
(14) Destri, S.; Ferro, D. R.; Khotina, I. A.; Porzio, W.; Farrina,
A. Macromol. Chem. Phys. 1998, 199, 1973.
Anal. Calcd for C52H58S8: C, 66.47; H, 6.22. Found: C, 65.41; H,
6.05.
Acknowledgements
Financial support from TFR and Carl Tryggers Stiftelse is gratefully
acknowledged. We specially thank Kurt Benkestock for performing
the MALDI-TOF experiments. Baron Jonas Leijonhufvud is
thanked for his wholehearted proof reading of the manuscript.
References
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Synthesis 2002, No. 9, 1195–1200 ISSN 0039-7881 © Thieme Stuttgart · New York