Push-pull-substituted oligo(2,5-thienyleneethynylene)s

Article abstract of DOI:10.1055/s-2006-926348

Oligo(2,5-thienyleneethynylene)s (OTE) with terminal donor-acceptor substitution were synthesized by applying Sonogashira-Hagihara reactions and a protection group technique. The combination of the alkylthio and nitro substituents provides a DAOTE series, whose long-wavelength absorption shows a monotonous bathochromic effect for increasing numbers n of repeat units. The convergence limit is already reached for n = 3. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-926348

PAPER
1009
Push–Pull-Substituted Oligo(2,5-thienyleneethynylene)s
P
ush-Pull-Substit
a
uted
O
ligo(
s
2,5-thieny
t
leneeth
i
ynylen
a
e)s n Mühling, Sonja Theisinger, Herbert Meier*
Institute of Organic Chemistry, University of Mainz, Duesbergweg 10–14, 55099 Mainz, Germany
Fax +49(6131)3925396; E-mail: hmeier@mail.uni-mainz.de
Received 2 August 2005; revised 10 October 2005
chemoselectively in 5-position with trimethylsilylacety-
lene (2) by applying the Sonogashira–Hagihara reaction
(Scheme 1). Compound 3, the product of the C(sp2)–C(sp)
coupling, was obtained in an almost quantitative yield.
Abstract: Oligo(2,5-thienyleneethynylene)s (OTE) with terminal
donor-acceptor substitution were synthesized by applying Sono-
gashira–Hagihara reactions and a protection group technique. The
combination of the alkylthio and nitro substituents provides a
DAOTE series, whose long-wavelength absorption shows a monot- The next step, namely the bromine/lithium exchange was
onous bathochromic effect for increasing numbers n of repeat units.
followed by the introduction of sulfur (3 → 4) and the
The convergence limit is already reached for n = 3.
alkylation with the butyl group (4 + 5a → 6a). The yield
Key words: alkynes, conjugation, coupling, heterocycles, sulfur
was disappointing when only the in situ formed 1-bro-
mobutane (3 + BuLi → 5a) reacted; however, additionally
added 5a enhanced the yield to about 70%. Deprotection
of 6a with K2CO3 afforded 7a, which could be used as
component for the donor end of the conjugated DAOTE
system.
Because of their interesting linear and nonlinear optical
(NLO) properties, donor-acceptor substituted conjugated
oligomers and polymers (D–p–A) have attracted a lot of
attention.1 Our recent studies on such systems were fo-
cussed on oligo(2,5-thienyleneethynylene)s (OTE)
(Figure 1). Different end-groups R1 and R2 such as
2,2¢:6¢,2¢¢-terpyridine,2,3 fullerene,4 fluorene5 and substi-
tuted benzene rings6 have been introduced in OTEs. In
continuation of our studies, we now became interested in
the preparation of push-pull-substituted compounds. The
Sonogashira–Hagihara reaction represents by far the most
usual access to the conjugated chains of aryleneethyn-
ylenes.1 This is also valid for 2,5-thienyleneethynylenes.2–15
The majority of OTEs contains solubilizing alkyl groups
attached to the thiophene rings. However, such groups en-
hance the torsional angles along the chain and therefore
impair the conjugation. These side chains can be aban-
doned for n £ 5, when solubilizing end-groups R1 or R2 or
both are present.
n-BuLi
S
Me3Si
H
2
a)
Br
Br
I
S
S
SiMe3
3 (98%)
1
C4H9Br
5a
_
C4H9S
S
S
S
SiMe3
SiMe3
6a (15–70%)
4
b)
C4H9S
S
H
7a (50%)
Scheme 1 Preparation of 2-butylthio-5-ethynylthiophene (7a):
Reagents and conditions: a) Pd(PPh3)2Cl2, PPh3, CuI, Et3N; b)
K2CO3, MeOH–CH2Cl2 (1:1).
S
S
R2
R1
We varied then the synthetic sequence and attached first
the alkylthio group to the thiophene ring (Scheme 2).
Thiophene (8) was lithiated and treated with elemental
sulfur6 (8 → 9) and subsequently with 1-iodododecane (9
+ 5b → 10).16 The oxidative iodination of 10 occurred se-
lectively in 5-position and the obtained compound 11 was
subjected to a Sonogashira–Hagihara reaction with 2. The
target component 7b was then formed by the deprotection
step 6b → 7b.
The convergent synthetic strategy for the DAOTE sys-
tems required then the use of extension reagent 12 and
endcapping reagent 13 (Scheme 3). The donor compo-
nents 7a,b reacted with 13 to 14a,b. The better solubiliz-
ing dodecyl group led thereby to a much better yield than
the butyl group. Because of this advantage, only 7b was
used for the extension of the conjugated chain. An alter-
nating sequence of Sonogashira–Hagihara reactions and
deprotection steps afforded the oligomers 15b, 16b, 18b,
n
OTE / PTE
Figure 1 Oligo- and poly(2,5-thienyleneethynylene)s
We decided to prepare donor-acceptor substituted oli-
go(2,5-thienyleneethynylene)s (DAOTE) with alkylthio
groups R1 and nitro groups R2. Long alkylthio groups are
weak electron donating, but highly solubilizing groups.
Moreover, they can be cleaved to thiols and fixed on gold
surfaces. Nitro groups are strong electron acceptors,
which reduce the solubility. We first tried the combination
C4H9S/NO2. 2-Bromo-5-iodothiophene (1) was reacted
SYNTHESIS 2006, No. 6, pp 1009–1015
Advanced online publication: 27.02.2006
DOI: 10.1055/s-2006-926348; Art ID: T10505SS
x
x
.
x
x
.2
0
0
6
© Georg Thieme Verlag Stuttgart · New York

1010
B. Mühling et al.
PAPER
C12H25
I
n-BuLi
_
I
Br
NO2
S
5b
SC12H25
S
S
S
S
SiMe3
C4H9S
S
S
12
13
9
10 (70%)
8
I2
S
S
HgO
2
NO2
13
S
S
7a
a)
a)
C12H25
S
I
SC12H25
S
14a (41%)
S
SiMe3
11 (60%)
6b (87%)
b)
C12H25
S
NO2
13
7b
C
12H25S
S
a)
H
14b (82%)
7b (89%)
a)
12
Scheme 2 Preparation of the donor component 7b: Reagents and
conditions: a) Pd(PPh3)2Cl2, PPh3, CuI, Et3N, toluene; b) K2CO3,
MeOH–CH2Cl2 (1:1).
C12H25
S
S
SiMe3
2
15b (95%)
19b, 21b and 22b. The compounds 16b, 19b and 22b,
which contain a free ethynyl group, were then end-cou-
pled with 13. The yield of the products 17b, 20b and 23b
decreased with increasing length of the chain (increasing
numbers n of repeat units).
b)
13
a)
C
12H25S
S
C12H25
S
S
NO2
S
H
The spectroscopic characterization of the compounds was
mainly based on 1H and 13C NMR measurements includ-
ing heteronuclear 2 D spectra (HMQC and HMBC).17
Figure 2 shows the assignment of the 1H and 13C chemical
shifts of 14b. The donor-acceptor substitution causes a
polarization, which is clearly documented by the Dd (13C)
values of the acetylenic carbon atoms. The 13C chemical
shifts are very sensitive towards partial charges. Exten-
sion of the conjugation (n = 2, 3, 4) leads to an increasing
distance of D and A and therefore to a decreasing interac-
tion of the partial dipole moments at the chain ends.1a,18,19
2
2
16b (93%)
17b (64%)
a)
12
C12H25
S
S
SiMe3
3
18b (47%)
b)
7.18
6.94
13
131.5
134.1
H
H
a)
C12H25S
S
C12H25
S
NO2
S
S
H
3
3
91.2
150.9
H
85.4
S
C
12H25S
19b (89%)
20b (48%)
NO2
122.7
141.0 S
_
δ+
δ
130.4
12
a)
H
7.79
7.10
128.6
130.8
1
Figure 2 Assignment of the H and 13C chemical shifts of 14b on
C12H25S
S
SiMe3
4
the basis of 2D-NMR measurements (HMQC and HMBC) in CDCl3
21b (66%)
b)
The uniform oligomeric structures of the two precursor
series 6b, 15b, 18b, 21b and 7b, 16b, 19b, 22b as well as
the target oligomer series 14b, 17b, 20b and 23b can be
best assessed by the 13C NMR data summarized in
Table 1.
13
a)
C12H25
S
S
C12H25
S
NO2
S
S
H
4
4
22b (93%)
23b (37%)
The intramolecular charge transfer (ICT) in the long-
wavelength absorption, the so-called charge transfer
band, provides a further criterion for the D–p–A interac-
tion. The effect is strong for the small distance of D and A
in 14b. Whereas dithienylacetylene (Figure 1,
R1 = R2 = H, n = 1) has in CHCl3 a lmax value of 317 nm,
Scheme 3 Preparation of the DAOTE series 14a,b; 17b; 20b; 23b:
a) Pd(PPh3)2Cl2, CuI, PPh3, NEt3, toluene; b) K2CO3, MeOH–CH2Cl2
(1:1).
Synthesis 2006, No. 6, 1009–1015 © Thieme Stuttgart · New York

PAPER
Push-Pull-Substituted Oligo(2,5-thienyleneethynylene)s
1011
Table 1 13C Chemical Shifts of the Precursor Oligomer Series 6b, 15b, 18b, 21b and 7b, 16b, 19b, 22b and the DAOTEs 14b, 17b, 20b and
23b (CDCl3/TMS, d)
Product sp2-C
CH
sp-C
CH
sp3-C
CH2
Cq
Cq
CH3
6b
132.0, 132.8
125.6, 137.4
97.1, 99.04
22.7, 28.4, 29.1, 29.3, 29.4, 29.5, –0.2, 14.1
29.6, 29.6, 29.7, 31.9, 38.9
15b
18b
21b
131.7, 132.1, 132.5,
132.7
124.0, 124.7, 125.0,
138.5
86.4, 86.7, 96.8,
100.5
22.6, 28.4, 29.1, 29.3, 29.4, 29.5, –0.2, 14.1
29.6, 29.6, 29.7, 31.9, 38.6
132.0, 132.1, 132.3,
132.6, 132.8, 132.8
123.7, 124.2, 124.6,
124.7, 125.3, 138.7
86.4, 86.6, 87.1,
87.4, 96.7, 100.7 29.6, 29.6, 29.6, 31.9, 38.6
22.6, 28.4, 29.1, 29.3, 29.4, 29.5, –0.2, 14.1
132.1, 132.1, 132.1,
132.4, 132.4, 132.4,
132.6, 132.8
123.6, 124.0, 124.4,
124.5, 124.6, 124.9,
125.3, 138.7
86.3, 86.5, 87.0,
87.2, 87.3, 87.5,
96.7, 100.7
22.6, 28.4, 29.1, 29.3, 29.4, 29.5, –0.3, 14.1
29.5, 29.6, 29.6, 31.9, 38.6
7b
131.9, 133.3,
124.4, 137.8
81.7
82.4
82.4
82.6
77.2
22.7, 28.4, 29.1, 29.3, 29.3, 29.4, 14.1
29.5, 29.6, 29.7, 31.9, 38.9
16b
19b
22b
131.6, 132.1, 132.7,
132.9
123.6, 124.6, 124.6,
138.6
76.5, 86.2, 86.8
22.6, 28.4, 29.1, 29.3, 29.4, 29.4, 14.1
29.5, 29.6, 29.7, 31.9, 38.6
132.0, 132.0, 132.1,
132.4, 132.8, 133.0
123.9, 124.0, 124.1,
124.6, 124.8, 138.7
76.3, 86.3, 86.7,
86.9, 87.4
22.6, 28.4, 29.1, 29.3, 29.4, 29.5, 14.1
29.5, 29.6, 29.7, 31.9, 38.5
132.1, 132.1, 132.1,
132.4, 132.4, 132.5,
132.8, 132.8
124.0, 124.1, 124.4,
124.5, 124.6, 124.9,
124.9, 138.7
76.3, 86.3, 86.6,
87.0, 87.0, 87.3,
87.4
22.7, 28.4, 29.1, 29.3, 29.4, 29.5, 14.1
29.5, 29.6, 29.6, 31.9, 38.6
14b
17b
20b
128.6, 130.8, 131.5,
134.1
122.7, 130.4, 141.0,
150.9
85.4, 91.2
22.7, 28.4, 29.1, 29.3, 29.4, 29.5, 14.1
29.6, 29.6, 29.7, 31.9, 38.4
128.6, 131.2, 132.0,
132.3, 132.7, 133.8
122.7, 123.9, 124.3,
129.8, 141.0, 150.8
85.8, 86.3, 86.8,
90.6
22.7, 28.4, 29.1, 29.3, 29.4, 29.5, 14.1
29.6, 29.6, 29.7, 31.9, 38.4
128.6, 131.2, 132.0,
132.3, 132.4, 132.5,
132.7, 133.8
122.7, 123.3, 123.9,
124.5, 125.1, 129.8,
141.0, 150.8
85.8, 86.3, 86.8,
87.5, 87.7, 90.6
22.7, 28.4, 29.1, 29.3, 29.4, 29.5, 14.1
29.6, 29.6, 29.7, 31.9, 38.5
23b
128.5, 131.2, 132.1,
132.1, 132.4, 132.5,
132.5, 123.7, 132.8,
133.7
122.9, 124.0, 124.1,
124.6, 124.9, 125.0,
126.1, 129.8, 138.8,
151.3
86.1, 86.3, 86.8,
86.9, 87.5, 87.5,
88.0, 90.8
22.7, 28.4, 29.1, 29.3, 29.4, 29.4, 14.1
29.5, 29.6, 29.7, 31.9, 38.6
14b exhibits an absorption maximum lmax = 413 nm. The
bathochromic shift decreases then very fast with increas-
ing conjugation (increasing numbers n of repeat units)
(Table 2 and Figure 3). The convergence value of the se-
ries l•= 428 1 nm is already reached for the trimer;1a,20
thus, the effective conjugation length nECL is extremely
low for a linearly conjugated system.18–22 Nevertheless,
the DAOTE series with terminal NO2 and SC12H25 groups
is a monotonous bathochromic series1a – in contrast to the
related DAOTE series with OCH3 groups as stronger do-
nor groups.1a,20
The UV/Vis spectra were obtained with a Zeiss MCS 320/340 spec-
trometer, the FT-IR spectra with a Perkin-Elmer GX/2000 spec-
trometer. The H and 13C NMR spectra were measured with the
Bruker spectrometers AC 200 and AMX 400. CDCl3 served as sol-
vent and TMS as internal standard. The FD-MS measurements were
performed on a Finnigan MAT 95 spectrometer. Silica gel (Merck,
1
Figure 3 Long-wavelength absorption maxima of the DAOTE se-
ries 14b, 17b, 20b, 23b in CHCl3 and their convergence to l•. [The
exponential fit corresponds to l(n) = l•–(l•–l1)e–2.12 (n–1)].
Synthesis 2006, No. 6, 1009–1015 © Thieme Stuttgart · New York

1012
B. Mühling et al.
PAPER
mL), the organic layer was dried (Na2SO4) and evaporated. Column
chromatography (3 × 30 cm SiO2, PE) afforded 1.44 g (15%) of a
viscous oil. The yield was enhanced to about 70% when equimolar
amounts of 5a were added after the addition of sulfur and stirring
was continued overnight at r.t.
Table 2 Long-Wavelength Absorption Maxima of the DAOTEs
14b, 17b, 20b, 23b in CHCl3
Compound
14b
n
1
2
3
4
l
max[nm]
e
max[cm2·mmol–1]
413
426
427
428
24.2 × 103
37.3 × 103
45.6 × 103
58.9 × 103
1H NMR (CDCl3): d = 0.25 (s, 9 H, CH3), 0.87 (t, 3J = 6.7 Hz, 3 H,
CH3), 1.32–1.44 (m, 2 H, CH2), 1.52–1.62 (m, 2 H, CH2), 2.80 (t,
17b
3
3J = 7.3 Hz, 2 H, SCH2), 7.05 (d, J = 3.3 Hz, 1 H, 3-H), 7.21 (d,
3J = 3.3 Hz, 1 H, 4-H).
20b
13C NMR (CDCl3): d = –0.2 [Si(CH3)3], 13.5 (CH3), 21.5 (CH2),
31.4 (CH2), 38.3 (SCH2), 85.0/85.4 (C≡C), 128.6 (C-5), 133.4,
133.5 (C-3, C-4), 144.1 (C-2).
23b
FD-MS: m/z (%) = 268 (100, M+).
70–230 mesh ASTM) was used for column chromatography. Petro-
leum ether (PE) used refers to the fraction boiling at 40–70 °C.
The compounds 1,23 1224 and 1324 were prepared according to liter-
ature; compounds 2, 5a, 5b and 8 are commercially available.
Anal. Calcd for C13H20S2Si (268.5): C, 58.15; H, 7.51; S, 23.88.
Found: C, 58.22; H, 7.43; S, 23.60.
2-Butylthio-5-ethynylthiophene (7a)
Following the general procedure B, 6a (1.44 g, 5.4 mmol) and
K2CO3 (0.85 g, 5.9 mmol) in CH2Cl2–MeOH (20 mL, 1:1) afforded
a colorless oil, which was purified by column chromatography
(4 × 40 cm SiO2, PE); yield: 0.53 g (50% based on 6a).
Sonogashira–Hagihara Coupling; General Procedure A
Equivalent amounts of iodine component and ethynyl component
were dissolved in an anhyd mixture of toluene and Et3N (about 1:1).
The solution was degassed and purged with argon. Pd(PPh3)2Cl2
(ca. 0.025 equiv), CuI (ca. 0.05 equiv) and PPh3 (ca. 0.05 equiv)
were added under argon. (Twofold amounts of catalysts did not
change the yields.) After stirring overnight at r.t., the volatile parts
were evaporated in vacuo and the residue was dissolved in CHCl3.
The solution was washed with equal volumes of aq sat. NH4Cl,
NaHCO3 and NaCl solutions. After drying (Na2SO4), the solvent
was removed and the residue purified by column chromatography
on SiO2. The solvent used for elution depended on the chain lengths
of the oligomer (see below). Solid products were purified by recrys-
tallization from the solvent mentioned for each product.
1H NMR (CDCl3): d = 0.88 (t, 3J = 6.7 Hz, 3 H, CH3), 1.33–1.44 (m,
3
2 H, CH2), 1.52–1.63 (m, 2 H, CH2), 2.80 (t, J = 7.3 Hz, 2 H,
SCH2), 3.34 (s, 1 H, C≡CH), 6.90 (d, 3J = 3.6 Hz, 1 H, 3-H), 7.10
(d, 3J = 3.6 Hz, 1 H, 4-H).
13C NMR (CDCl3): d = 14.1 (CH3), 21.5 (CH2), 31.4 (CH2), 38.3
(SCH2), 77.2/81.7 (C≡C), 124.4 (C-5), 131.9, 133.3 (C-3, C-4),
137.8 (C-2).
FD-MS: m/z (%) = 196 (100, M+).
Anal. Calcd for C10H12S2 (196.3): C, 61.18; H, 6.16; S, 32.66.
Found: C, 61.34; H, 6.08; S, 32.50.
Deprotection of the Ethynyl Groups; General Procedure B
To the trimethylsilylethynyl compound (1 equiv) dissolved in
CH2Cl2–MeOH (1:1), was added K2CO3 (ca. 1.1 equiv). The stirred
reaction mixture was kept at r.t. until the TLC (SiO2/toluene) indi-
cated the end of the cleavage. The solvent was removed in vacuo,
the residue dissolved in CHCl3, washed with H2O (3 ×) and dried
(Na2SO4). Evaporation led to the crude product, which was purified
by column chromatography (SiO2/solvent described for each case)
and/or recrystallization.
2-(Dodecylthio)thiophene (10)
To thiophene (8; 5.0 g, 59.5 mmol) in anhyd THF (20 mL), was add-
ed dropwise a 2.5 M solution of n-BuLi in n-hexane (23.8 mL, 59.5
mmol) at –10 °C. After stirring for 1 h under argon, powdered sulfur
(2.56 g, 80.0 mmol) was added and the mixture warmed within 2 h
to r.t. 1-Iodododecane (5b; 17.6 g, 59.5 mmol) was added and the
stirring continued for 16 h. The volatile parts of the reaction mixture
were evaporated and the residue was dissolved in CH2Cl2. The fil-
tered solution was extracted with H2O (3 × 50 mL), dried (Na2SO4)
and distilled to give a viscous oil; yield: 10.5 g (70%); bp 154 °C/
200 Pa.
2-Bromo-5-(trimethylsilylethynyl)thiophene (3)
A mixture of 1 (30.00 g, 104 mmol), 2 (10.3 g, 105 mmol),
Pd(PPh3)2Cl2 (1.03 g, 2.6 mmol), CuI (0.99 g, 5.2 mmol) and PPh3
(1.36 g, 5.2 mmol) was reacted in toluene/Et3N (130 mL) according
to the general procedure A. Column chromatography (10 × 20 cm
SiO2, PE) yielded 26.32 g (98%) of a viscous oil.
1H NMR (CDCl3): d = 0.23 (s, 9 H, CH3), 6.87/6.94 (AB, 3J = 4.0
Hz, 2 H, 3-H, 4-H).
1H NMR (CDCl3): d = 0.88 (t, 3J = 6.6 Hz, 3 H, CH3), 1.12–1.38 (m,
3
18 H, CH2), 1.54–1.63 (m, 2 H, CH2), 2.77 (t, J = 7.4 Hz, 2 H,
3
3
SCH2), 6.94 (dd, J = 5.4 Hz, J = 3.7 Hz, 1 H, 4-H), 7.08 (dd,
4
3
3J = 3.7 Hz, J = 1.1 Hz, 1 H, 3-H), 7.29 (dd, J = 5.4 Hz, 4J = 1.1
Hz, 1 H, 5-H).
13C NMR (CDCl3): d = 14.1 (CH3), 22.7, 28.4, 28.5, 29.1, 29.3,
29.4, 29.5, 29.6, 29.7, 31.9 (CH2), 38.9 (SCH2), 127.4 (C-3), 128.8
(C-5), 133.1 (C-4), 135.1 (C-2).
13C NMR (CDCl3): d = –0.2 (CH3), 96.4, 101.1 (C≡C), 113.1 (C-2),
125.0 (C-5), 129.8, 132.8 (C-3, C-4).
FD-MS: m/z (%) = 284 (100, M+).
FD-MS: m/z (%) = 260/258 (100, M+, Br isotope pattern).
Anal. Calcd for C16H28S2 (284.5): C, 67.54; H, 9.92; S, 22.54.
Found: C, 67.67; H, 9.85; S, 22.42.
Anal. Calcd for C9H11BrSSi (259.2): C, 41.70; H, 4.28; S, 12.37.
Found: C, 41.31; H, 3.96; S, 12.50.
2-Dodecylthio-5-iodothiophene (11)
2-Butylthio-5-(trimethylsilylethynyl)thiophene (6a)
To compound 10 (1.0 g, 3.5 mmol) in anhyd benzene (10 mL), were
slowly added yellow HgO (0.77 g, 3.5 mmol) and I2 (0.92 g, 3.6
mmol) at 0 °C. The mixture was vigorously stirred till the color
(caused by the I2) faded, filtered and the solvent removed. Purifica-
tion by column chromatography (5 × 30 cm SiO2, PE) yielded 0.87
g (60%) of a yellow oil.
To 2-bromo-5-(trimethylsilylethynyl)thiophene (3; 9.0 g, 34.7
mmol) in anhyd Et2O (25 mL), was added dropwise a 2.5 M solution
of n-BuLi in n-hexane (13.8 mL, 34.7 mmol) at –78 °C. After stir-
ring for 1 h under argon, powdered sulfur (1.4 g, 43.7 mmol) was
added and the reaction stopped after 2 h at 0 °C. H2O (10 mL) was
slowly added and the mixture stirred for 30 min. To the filtered mix-
ture was added CH2Cl2 (50 mL). After extraction with H2O (2 × 50
Synthesis 2006, No. 6, 1009–1015 © Thieme Stuttgart · New York

PAPER
Push-Pull-Substituted Oligo(2,5-thienyleneethynylene)s
1013
1H NMR (CDCl3): d = 0.87 (t, 3J = 6.7 Hz, 3 H, CH3), 1.12–1.38 (m,
mmol) in a Et3N (20 mL, 14.52 g, 143 mmol)/toluene (20 mL) af-
forded a viscous red oil, which was purified by column chromatog-
raphy (4 × 40 cm SiO2, PE–CH2Cl2, 1:1); yield: 0.40 g (82%).
IR (neat): 2189 cm–1 (C≡C).
3
18 H, CH2), 1.53–1.64 (m, 2 H, CH2), 2.74 (t, J = 7.4 Hz, 2 H,
SCH2), 6.76 (d, 3J = 3.7 Hz, 1 H, 3-H), 7.06 (d, 3J = 3.7 Hz, 1 H, 4-
H).
13C NMR (CDCl3): d = 14.1 (CH3), 22.7/28.3/28.3/29.1/29.3/29.4/
29.5/29.6/29.6/31.9 (CH2), 39.1 (SCH2), 75.1 (C-5), 134.8 (C-3),
137.4 (C-4), 140.6 (C-2).
1H NMR (CDCl3): d = 0.85 (t, 3J = 6.7 Hz, 3 H, CH3), 1.12–1.37 (m,
3
18 H, CH2), 1.59–1.69 (m, 2 H, CH2), 2.84 (t, J = 7.4 Hz, 2 H,
SCH2), 6.94 (d, 3J = 3.9 Hz, 1 H, 4-Hthienyl), 7.10 (d, 3J = 4.4 Hz, 1
H, 3-H), 7.18 (d, 3J = 3.9 Hz, 1 H, 3-Hthienyl), 7.79 (d, 3J = 4.4 Hz, 1
H, 4-H).
FD-MS: m/z (%) = 410 (100, M+).
Anal. Calcd for C16H27IS2 (410.4): C, 46.82; H, 6.63; S, 15.62.
Found: C, 46.59; H, 6.74; S, 15.55.
FD-MS: m/z (%) = 435 (100, M+).
Anal. Calcd for C22H29NO2S3 (435.7): C, 60.65; H, 6.71; N, 3.21; S,
22.08. Found: C, 60.48; H, 6.97; N, 3.14; S, 21.98.
2-Dodecylthio-5-(trimethylsilylethynyl)thiophene (6b)
Following the general procedure A, a mixture of 11 (0.51 g, 1.24
mmol), 2 (0.12 g, 1.24 mmol), Pd(PPh3)2Cl2 (11.8 mg, 0.03 mmol),
CuI (11.8 mg, 0.06 mmol), PPh3 (16.3 mg, 0.06 mmol) and Et3N (5
mL, 3.63 g, 35.87 mmol) in toluene (5 mL) yielded 6b as a viscous
colorless oil. Column chromatography (3 × 40 cm SiO2, PE) afford-
ed 0.50 g (87%) of analytically pure product.
1H NMR (CDCl3): d = 0.24 [s, 9 H, Si(CH3)3], 0.87 (t, 3J = 6.7 Hz,
3 H, CH3), 1.12–1.38 (m, 18 H, CH2), 1.50–1.63 (m, 2 H, CH2), 2.79
(t, 3J = 7.4 Hz, 2 H, SCH2), 7.05 (d, 3J = 3.3 Hz, 1 H, 3-H), 7.21 (d,
3J = 3.3 Hz, 1 H, 4-H).
2-[5-(Dodecylthio)thien-2-ylethynyl]-5-trimethylsilylethynyl-
thiophene (15b)
Following the general procedure A, a mixture of 7b (200 mg, 0.65
mmol), 12 (190 mg, 0.65 mmol), Pd(PPh3)2Cl2 (6.3 mg, 0.016
mmol), CuI (6.1 mg, 0.032 mmol) and PPh3 (8.4 mg, 0.032 mmol)
in Et3N (5 mL, 3.63 g, 35.87 mmol)/toluene (5 mL) afforded a yel-
lowish viscous oil, which was purified by column chromatography
(8 × 25 cm SiO2, PE–CH2Cl2, 2:1); yield: 300 mg (95%).
1H NMR (CDCl3): d = 0.23 [s, 9 H, Si(CH3)3], 0.86 (t, 3J = 6.6 Hz,
3 H, CH3), 1.12–1.37 (m, 18 H, CH2), 1.57–1.67 (m, 2 H, CH2), 2.81
(t, 3J = 7.4 Hz, 2 H, SCH2), 6.92 (d, 3J = 3.7 Hz, 1 H, 4-Hthienyl), 7.04
(d, 3J = 3.9 Hz, 1 H, 3-H), 7.07 (d, 3J = 3.9 Hz, 1 H, 4-H), 7.10 (d,
3J = 3.7 Hz, 1 H, 3-Hthienyl).
FD-MS: m/z (%) = 380 (100, M+).
Anal. Calcd for C21H36S2Si (380.7): C, 66.25; H, 9.53; S, 16.84.
Found: C, 66.06; H, 9.67; S, 16.58.
2-Dodecylthio-5-ethynylthiophene (7b)
FD-MS: m/z (%) = 486 (100, M+).
Reaction of 6b (2.10 g, 5.52 mmol) and K2CO3 (0.84 g, 6.06 mmol)
in MeOH–CH2Cl2 (20 mL, 1:1) afforded – according to the general
procedure B described above – a viscous oil, which was purified by
column chromatography (8 × 30 cm SiO2, PE); yield: 1.51 g (89%).
Anal. Calcd for C27H38S3Si (486.9): C, 66.61; H, 7.87; S, 19.76.
Found: C, 66.49; H, 7.68; S, 19.56.
2-[5-(Dodecylthio)thien-2-ylethynyl]-5-ethynylthiophene (16b)
Following the general procedure B, reaction of 15b (300 mg, 0.62
mmol) with K2CO3 (90 mg, 0.65 mmol) in MeOH–CH2Cl2 (20 mL,
1:1) afforded a yellowish viscous oil, which was purified by column
chromatography (8 × 30 cm SiO2, PE–CH2Cl2, 3:1); yield: 240 mg
(93%).
1H NMR (CDCl3): d = 0.87 (t, 3J = 6.8 Hz, 3 H, CH3), 1.12–1.38 (m,
3
18 H, CH2), 1.50–1.64 (m, 2 H, CH2), 2.79 (t, J = 7.4 Hz, 2 H,
SCH2), 3.33 (s, 1 H, C≡CH), 6.89 (d, 3J = 3.7 Hz, 1 H, 3-H), 7.09
(d, 3J = 3.7 Hz, 1 H, 4-H).
FD-MS: m/z (%) = 308 (100, M+).
1H NMR (CDCl3): d = 0.86 (t, 3J = 6.7 Hz, 3 H, CH3), 1.11–1.36 (m,
Anal. Calcd for C18H28S2 (308.5): C, 70.07; H, 9.15; S, 20.78.
Found: C, 69.89; H, 9.22; S, 20.66.
3
18 H, CH2), 1.57–1.67 (m, 2 H, CH2), 2.81 (t, J = 7.4 Hz, 2 H,
3
SCH2), 3.36 (s, 1 H, C≡CH), 6.93 (d, J = 4.1 Hz, 1 H, 4-Hthienyl),
7.07 (d, 3J = 3.7 Hz, 1 H, 3-H), 7.10 (d, 3J = 4.1 Hz, 1 H, 3-Hthienyl),
7.12 (d, 3J = 3.7 Hz, 1 H, 4-H).
2-[5-(Butylthio)thien-2-ylethynyl]-5-nitrothiophene (14a)
Following the general procedure A, a mixture of 7a (0.53 g, 2.7
mmol), 13 (0.56 g, 2.7 mmol), Pd(PPh3)2Cl2 (0.028 g, 0.07 mmol),
CuI (0.026 g, 0.14 mmol), PPh3 (0.037 g, 0.14 mmol) in Et3N–tolu-
ene (12 mL, 1:1) afforded a red oil, which was purified by column
chromatography (3 × 50 cm SiO2, PE); yield: 0.36 g (41%).
FD-MS: m/z (%) = 414 (100, M+).
Anal. Calcd for C24H30S3 (414.7): C, 69.51; H, 7.29; S, 23.20;
Found: C, 69.38; H, 7.22; S, 23.08.
IR (neat): 2189 cm–1 (C≡C).
Dimer 17b
Following the general procedure A, a mixture of 16b (0.25 g, 0.60
mmol), 13 (0.13 g, 0.60 mmol), Pd(PPh3)2Cl2 (5.9 mg, 0.015
mmol), CuI (5.5 mg, 0.029 mmol), PPh3 (7.9 mg, 0.03 mmol) in
Et3N (5 mL, 3.63 g, 35.87 mmol)/toluene (5 mL) afforded red crys-
tals, which were purified by column chromatography (3 × 40 cm
SiO2, PE–CH2Cl2, 1:1) and recrystallization from PE; yield: 0.21 g
(64%); mp 38 °C.
IR (KBr): 2184 cm–1 (C≡C).
1H NMR (CDCl3): d = 0.85 (t, 3J = 6.7 Hz, 3 H, CH3), 1.10–1.37 (m,
18 H, CH2), 1.57–1.68 (m, 2 H, CH2), 2.84 (t, J = 7.4 Hz, 2 H,
1H NMR (CDCl3): d = 0.89 (t, 3J = 6.7 Hz, 3 H, CH3), 1.37–1.47 (m,
3
2 H, CH2), 1.55–1.65 (m, 2 H, CH2), 2.86 (t, J = 7.4 Hz, 2 H,
SCH2), 6.95 (d, 3J = 3.8 Hz, 1 H, 4-Hthienyl), 7.10 (d, 3J = 4.4 Hz, 3-
H), 7.19 (d, 3J = 3.8 Hz, 1 H, 3-Hthienyl), 7.80 (d, 3J = 4.4 Hz, 1 H, 4-
H).
13C NMR (CDCl3): d = 13.5 (CH3), 21.6 (CH2), 31.4 (CH2), 38.1
(SCH2), 85.4, 91.2 (C≡C), 122.8, 130.4, 140.9, 150.9 (Cq), 128.6,
130.8, 131.6, 134.1 (CH).
FD-MS: m/z (%) = 323 (100, M+).
3
3
Anal. Calcd for C14H13NO2S3 (323.5): C, 51.99; H, 4.05; S, 29.74.
Found: C, 52.04; H, 4.08; S, 29.88.
SCH2), 6.94/7.10 (AB, J = 4.1 Hz, 2 H, thiophene, donor side),
7.18 (m, 2 H, thiophene, center), 7.18/7.80 (AB, J = 4.4 Hz, 2 H,
3
thiophene, acceptor side).
FD-MS: m/z (%) = 542 (100, M+).
2-[5-(Dodecylthio)thien-2-ylethynyl]-5-nitrothiophene (14b)
Following the general procedure A, a mixture of 7b (0.36 g, 1.16
mmol), 13 (0.24 g, 1.16 mmol), Pd(PPh3)2Cl2 (11.2 mg, (0.028
mmol), CuI (10.7 mg, 0.056 mmol), and PPh3 (14.7 mg, 0.056
Anal. Calcd for C28H31NO2S4 (541.8): C, 62.07; H, 5.77; N, 2.59; S,
23.67. Found: C, 61.89; H, 5.79; N, 2.34; S, 23.78.
Synthesis 2006, No. 6, 1009–1015 © Thieme Stuttgart · New York

1014
B. Mühling et al.
PAPER
Trimer 18b
cedure B afforded yellow crystals which were recrystallized from
CH2Cl2–MeOH (1:1); yield: 53 mg (85%); mp 93 °C.
Following the general procedure A, a mixture of 16b (0.13 g, 0.31
mmol), 12 (0.10 g, 0.31 mmol), Pd(PPh3)2Cl2 (3.1 mg, 0.008
mmol), CuI (2.9 mg, 0.015 mmol), PPh3 (3.9 mg, 0.015 mmol) in
Et3N (5 mL, 3.63 g, 35.87 mmol)/toluene (5 mL) afforded yellow
crystals, which were purified by column chromatography (8 × 25
cm SiO2, PE–CH2Cl2, 9:1); yield: 0.09 g (47%); mp 84 °C.
1H NMR (CDCl3): d = 0.24 (s, 9 H, CH3), 0.86 (t, 3J = 6.7 Hz, 3 H,
CH3), 1.12–1.36 (m, 18 H, CH2), 1.57–1.68 (m, 2 H, CH2), 2.82 (t,
3J = 7.3 Hz, 2 H, SCH2), 6.93/7.12 (AB, 3J = 3.7 Hz, 2 H, SC12H25-
substituted thiophene ring), 7.08 (‘s’, 2 H, central thiophene ring),
7.11/7.13 (AB 3J = 3.7 Hz, 2 H, thiophene).
1H NMR (CDCl3): d = 0.85 (t, 3J = 6.6 Hz, 3 H, CH3), 1.10–1.36 (m,
3
18 H, CH2), 1.58–1.68 (m, 2 H, CH2), 2.82 (t, J = 7.4 Hz, 2 H,
SCH2), 3.38 (s, 1 H, C≡C), 6.94/7.15 (AB, 3J = 4.0 Hz, 2 H,
C12H25S-substituted thiophene ring), 7.11–7.16 (m, 6 H, thiophene
rings).
Anal. Calcd for C36H34S5 (627.0): C, 68.97; H, 5.47; S, 25.57.
Found: C, 68.80; H, 5.65; S, 25.49.
Tetramer 23b
A mixture of 22b (58.6 mg, 0.09 mmol), 13 (19.5 mg, 0.09 mmol),
Pd(PPh3)2Cl2 (0.8 mg, 0.002 mmol), CuI (0.9 mg, 0.005 mmol), and
PPh3 (1.3 mg, 0.005 mmol) was reacted in Et3N (5 mL, 3.63 g, 35.87
mmol)/toluene (5 mL) according to the general procedure A. Puri-
fication by column chromatography (8 × 20 cm SiO2, PE–CH2Cl2
1:3) and recrystallization from CH2Cl2–MeOH (1:1) yielded 26 mg
(37%) red crystals; mp 117 °C.
Anal. Calcd for C33H40S4Si (593.0): C, 66.84; H, 6.80; S, 21.63.
Found: C, 66.73; H, 6.92; S, 21.70.
Trimer 19b
Cleavage of 18b (0.088 g, 0.15 mmol) with K2CO3 (0.023 g, 0.16
mmol) in CH2Cl2–MeOH (10 mL, 1:1) according to the general pro-
cedure B, gave 0.080 g (98%) of 19b. Recrystallization from the
same solvent mixture yielded yellow crystals; mp 62 °C.
IR (KBr): 2176 cm–1 (C≡C).
1H NMR (CDCl3): d = 0.86 (t, 3J = 6.6 Hz, 3 H, CH3), 1.09–1.37 (m,
1H NMR (CDCl3): d = 0.86 (t, 3J = 6.7 Hz, 3 H, CH3), 1.11–1.35 (m,
3
18 H, CH2), 1.58–1.69 (m, 2 H, CH2), 2.82 (t, J = 7.4 Hz, 2 H,
3
18 H, CH2), 1.57–1.68 (m, 2 H, CH2), 2.81 (t, J = 7.4 Hz, 2 H,
3
SCH2), 6.94 (d, J = 3.7 Hz, 1 H, C12H25S-substituted thiophene
SCH2), 3.36 (s, 1 H, C≡CH), 6.94 (d, 3J = 3.7 Hz, 1 H, C12H25S-sub-
3
ring), 7.81 (d, J = 4.4 Hz, 1 H, NO2-substituted thiophene ring),
stituted thiophene ring), 7.10–7.15 (m, 5 H, thiophene rings).
7.12–7.23 (m, 8 H, remaining H of thiophene rings).
FD-MS: m/z (%) = 754 (100, [M + H+]).
FD-MS: m/z (%) = 520 (100, M+).
Anal. Calcd for C30H32S4 (520.8): C, 69.18; H, 6.19; S, 24.62.
Found: C, 69.03; H, 6.30; S, 24.55.
Anal. Calcd for C40H35NO2S6 (754.1): C, 63.71; H, 4.68; N, 1.86; S,
25.51. Found: C, 63.57; H, 4.77; N, 1.69; S, 25.24.
Trimer 20b
A mixture of 19b (0.25 g, 0.60 mmol), 13 (0.13 g, 0.60 mmol),
Pd(PPh3)2Cl2 (5.9 mg, 0.015 mmol), CuI (5.5 mg, 0.029 mmol) and
PPh3 (7.9 mg, 0.030 mmol) was reacted in Et3N (5 mL, 3.63 g, 35.87
mmol)/toluene (5 mL) according to the general procedure A. Col-
umn chromatography (3 × 40 cm SiO2, PE–CH2Cl2, 1: 1) and re-
crystallization of the product from PE afforded 0.21 g (48%) of red
crystals; mp 76 °C.
Acknowledgment
We are grateful to the Deutsche Forschungsgemeinschaft and the
Fonds der Chemischen Industrie for the financial support.
References
IR (KBr): 2180 cm–1 (C≡C).
(1) (a) Meier, H. Angew. Chem. Int. Ed. 2005, 44, 2482; Angew.
Chem. 2005, 117, 2536; and references cited therein.
(b) Martin, R. E.; Diederich, F. Angew. Chem. Int. Ed. 1999,
38, 1350; Angew. Chem. 1999, 111, 1440. (c) Electronic
Materials: The Oligomer Approach; Müllen, K.; Wegner,
G., Eds.; Wiley-VCH: Weinheim, 1998.
1H NMR (CDCl3): d = 0.85 (t, 3J = 6.7 Hz, 3 H, CH3), 1.12–1.38 (m,
3
18 H, CH2), 1.58–1.70 (m, 2 H, CH2), 2.84 (t, J = 7.4 Hz, 2 H,
SCH2), 6.94/7.10 (AB, 3J = 4.1 Hz, 2 H, C12H25S-substituted
thiophene ring), 7.16 (m, 4 H, inner thiophene rings), 7.16/7.80
(AB, 3J = 4.4 Hz, 2 H, NO2-substituted thiophene ring).
(2) Ringenbach, C.; De Nicola, A.; Ziessel, R. J. Org. Chem.
FD-MS: m/z (%) = 648 (100, [M + H+]).
2003, 68, 4708.
(3) De Nicola, A.; Ringenbach, C.; Ziessel, R. Tetrahedron Lett.
2003, 44, 183.
(4) Obara, Y.; Takimiya, K.; Aso, Y.; Otsubo, T. Tetrahedron
Lett. 2001, 42, 6877.
(5) Wu, R.; Schumm, J. S.; Pearson, D. L.; Tour, J. M. J. Org.
Chem. 1996, 61, 6906.
(6) Pearson, D. L.; Tour, J. M. J. Org. Chem. 1997, 62, 1376.
(7) Fujitsuka, M.; Makinoshima, T.; Ito, O.; Obara, Y.; Aso, T.;
Otsubo, T. J. Phys. Chem. B 2003, 107, 739.
(8) Li, J.; Liao, L.; Pang, Y. Tetrahedron Lett. 2002, 43, 391.
(9) Pearson, D. L.; Jones, L. II; Schumm, J. S.; Tour, J. M.
Synth. Met. 1997, 84, 303.
Anal. Calcd for C34H33NO2S5 (648.0): C, 63.03; H, 5.13; N, 2.16; S,
24.74. Found: C, 62.88; H, 5.39; N, 2.34; S, 24.70.
Tetramer 21b
A mixture of 19b (0.077 g, 0.15 mmol), 12 (0.046 g, 0.15 mmol),
Pd(PPh3)2Cl2 (1.6 mg, 0.004 mmol), CuI (1.5 mg, 0.008 mmol), and
PPh3 (2.1 mg, 0.008 mmol) was reacted according to the general
procedure A in Et3N (5 mL, 3.63 g, 35.87 mmol)/toluene (5 mL).
Column chromatography (8 × 30 cm SiO2, PE–CH2Cl2, 3:1) afford-
ed 0.069 g (66%) of yellow crystals; mp 109 °C.
1H NMR (CDCl3): d = 0.22 (s, 9 H, CH3), 0.86 (t, 3J = 6.7 Hz, 3 H,
CH3), 1.10–1.37 (m, 18 H, CH2), 1.56–1.66 (m, 2 H, CH2), 2.82 (t,
3J = 7.4 Hz, 2 H, SCH2), 6.94/7.15 (AB, 3J = 3.7 Hz, 2 H, C12H25S-
substituted thiophene ring), 7.08–7.16 (m, 6 H, thiophene rings).
(10) Samuel, I. D. W.; Ledoux, I.; Delporte, C.; Pearson, D. L.;
Tour, J. M. Chem. Mater. 1996, 8, 819.
(11) Geisler, T.; Petersen, J. C.; Bjoernholm, T.; Fischer, E.;
Larsen, J.; Dehn, C.; Brédas, J.-L.; Tormos, G. V.; Nugara,
P. N.; Lakshikantham, M. V.; Cava, M. P. Synth. Met. 1993,
53, 271.
Anal. Calcd for C39H42S5Si (699.2): C, 67.00; H, 6.05; S, 22.93
Found: C, 66.85; H, 5.95; S, 23.02
(12) Pearson, D. L.; Schumm, J. S.; Tour, J. M. Macromolecules
1994, 27, 2348.
Tetramer 22b
Cleavage of 21b (69 mg, 0.10 mmol) with K2CO3 (15 mg, 0.11
mmol) in CH2Cl2–MeOH (10 mL, 1:1) according to the general pro-
Synthesis 2006, No. 6, 1009–1015 © Thieme Stuttgart · New York

PAPER
Push-Pull-Substituted Oligo(2,5-thienyleneethynylene)s
1015
(13) Tormos, G. V.; Nugara, P. N.; Lakshikantham, M. V.; Cava,
M. P. Synth. Met. 1993, 53, 271.
(14) Carpita, A.; Lessi, A.; Rossi, R. Synthesis 1984, 571.
(15) Bunz, U. H. F. Chem. Rev. 2000, 100, 1605; and references
cited therein.
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(17) HMQC and HMBC contour plots for 14a are depicted in:
Hesse, M.; Meier, H.; Zeeh, B. Spektroskopische Methoden
in der organischen Chemie, 7th ed.; Thieme: Stuttgart, 2005,
193.
(18) Meier, H.; Gerold, J.; Kolshorn, H.; Mühling, B. Chem. Eur.
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(20) Mühling, B. Ph.D. Dissertation; University of Mainz:
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379.
(22) Ickenroth, D.; Weissmann, S.; Rumpf, N.; Meier, H. Eur. J.
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(24) Meier, H.; Mühling, B.; Oehlhof, A.; Theisinger, S.; Kirsten,
E. Eur. J. Org. Chem. 2006, 405.
Synthesis 2006, No. 6, 1009–1015 © Thieme Stuttgart · New York