Symmetrical and nonsymmetrical liquid crystalline oligothiophenes: Convenient synthesis and transition-temperature engineering

Article abstract of DOI:10.1002/ejoc.200600850

Two approaches to transition-temperature engineering in liquid crystalline oligothiophenes are described: (i) substitution at the aromatic core with two identical branched alkyl chains and (ii) desymmetrization of the molecule with two alkyl substituents of different length or structure. Key steps in the synthesis of symmetrical and nonsymmetrical terthiophenes and quaterthiophenes involve Suzuki coupling and carbanion alkylation. A well-adjusted balance between the π-π stacking of the aromatic core and the disorder caused by the peripheral alkyl chains is demonstrated to be important for the control of the thermotropic behavior of oligothiophene mesogens. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejoc.200600850

FULL PAPER
DOI: 10.1002/ejoc.200600850
Symmetrical and Nonsymmetrical Liquid Crystalline Oligothiophenes:
Convenient Synthesis and Transition-Temperature Engineering
Julie Leroy,[a] Nicolas Boucher,[b] Sergey Sergeyev,[a] Michele Sferrazza,[b] and
Yves Henri Geerts*[a]
Keywords: Oligothiophenes / Semiconductors / Liquid crystals / Transition-temperature engineering / Cross-coupling
Two approaches to transition-temperature engineering in li-
quid crystalline oligothiophenes are described: (i) substitu-
tion at the aromatic core with two identical branched alkyl
chains and (ii) desymmetrization of the molecule with two
alkyl substituents of different length or structure. Key steps
in the synthesis of symmetrical and nonsymmetrical ter-
thiophenes and quaterthiophenes involve Suzuki coupling
and carbanion alkylation. A well-adjusted balance between
the π–π stacking of the aromatic core and the disorder caused
by the peripheral alkyl chains is demonstrated to be impor-
tant for the control of the thermotropic behavior of oligo-
thiophene mesogens.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
molecular-weight liquid crystalline semiconductors are eas-
ily processible from solution and can therefore be consid-
ered as realistic candidates for large-area organic electronic
devices.
Introduction
Oligothiophenes have been attracting increasing atten-
tion due to their high charge-carrier mobility (µ), which is
a key feature for materials used in organic electronic devices
such as organic field-effect transistors (OFETs).[1] Among
other oligothiophene derivatives, symmetrical α,αЈ-disubsti-
tuted oligothiophenes show enhanced chemical and electro-
chemical stability.[2] In addition, a combination of a rigid
aromatic core and flexible side chains in the structure of
α,αЈ-dialkyloligothiophenes induces the formation of liquid
crystalline mesophases.[3] The practical application of poly-
crystalline materials in OFETs is often hampered by struc-
tural defects and grain-boundary effects, which dramati-
cally decrease the charge-carrier mobility.[4] In contrast, li-
quid crystals have been recognized as a new type of organic
semiconductors, as they are capable of self-healing struc-
tural defects and of self-organization in large structurally
homogeneous domains.[5] Furthermore, it was shown that
the influence of domain boundaries, if any, on carrier trans-
port in liquid crystalline phases is very small.[6] Funahashi
and Hanna reported higher temperature-independent
charge-carrier mobility (µ = 10–2 cm2 V–1 s–1) in the ordered
SmG phase of dioctylterthiophene 1a relative to that (µ =
10–3 cm2 V–1 s–1) in the crystalline phase.[7] In addition, low-
Our current research aim is to design oligothiophenes
with thermotropic properties suitable for OFET applica-
tions and to reach a better understanding of the relation-
ship between their molecular structure and phase order.
Fabrication of realistic organic electronic devices such as
OFETs requires ambient-temperature liquid crystalline
semiconductors. On the other hand, the stability of me-
sophases in a temperature range that is as broad as possible
is also crucially important for device performance. How-
ever, the prediction of phase behavior from the chemical
structure of oligothiophenes is still hardly possible. The
major principle in the design of new mesogens consists of
a compromise between the order caused by the π–π stacking
of the flat aromatic cores and the disorder induced by the
flexible peripheral substituents. The transition between the
crystalline (Cr) and liquid crystalline (LC) phases involves
the conformational disordering of the side chains, also re-
ferred to as “side-chain melting”.[8] In agreement with this
simple model, symmetrical 5,5ЈЈ-bis(n-alkyl)terthiophenes
with six to nine carbon atoms in the alkyl chain demon-
strate increasing Cr–LC transition temperatures with in-
creasing chain length,[3,9] i.e., the same tendency as that of
the melting points of linear alkanes. On the other hand,
it has been well documented that branching of peripheral
substituents results in the lowering of the Cr–LC transition
temperatures of discotic mesogens.[8,10] Here, we explore
two different possibilities of tuning the transition tempera-
ture in liquid crystalline terthiophenes and quaterthiophenes:
substitution at the aromatic core with two identical
[a] Laboratoire de Chimie des Polymères, CP 206/01, Université
Libre de Bruxelles,
Boulevard du Triomphe, 1050 Bruxelles, Belgium
Fax: +32-2-6505410
E-mail: ygeerts@ulb.ac.be
[b] Département de Physique, CP 223, Université Libre de Brux-
elles,
Boulevard du Triomphe, 1050 Bruxelles, Belgium
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
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Symmetrical and Nonsymmetrical Liquid Crystalline Oligothiophenes
FULL PAPER
branched alkyl chains and desymmetrization of the mole- were prepared (Scheme 1). As expected, haloalkanes in
cule with two alkyl substituents of different length or struc- which the branching site was remote from the halogen atom
ture.
did not cause any changes in reactivity relative to that of
their linear analogs: 1c and 1d were isolated in 88–90%
yield. 1H NMR spectra of the crude product indicated only
traces of the starting material and no monoalkylterthio-
phenes. In addition, the symmetrical dialkylquaterthio-
phene 5 was prepared by the same method from quaterthio-
phene 4 in 85% yield.
Results and Discussion
Synthesis
A four-step synthesis of symmetrical 2,5ЈЈ-dialkylterthio-
We also attempted to extend this method to the synthesis
phenes (such as 1a,b) was reported earlier by Byron et al.[3] of nonsymmetrical dialkylterthiophenes by sequential alky-
Repeated Friedel–Crafts acylation with the corresponding lation with two different haloalkanes. However, alkylation
acyl chloride followed by Wolff–Kishner–Huang–Minlon of terthiophene 3 with 1 equiv. of 1-iodooctane resulted in
reduction afforded the target molecules in rather low yield a mixture of the monooctylterthiophene 6a, the dioctylter-
(15–30% starting from terthiophene 3). More recently, thiophene 1a, and the starting material. We explain this by
Kirchmeyer and co-workers reported on the large-scale syn- the higher solubility, and therefore higher reactivity, of the
thesis of didecyl oligothiophenes from the appropriate thio- monoanion of 6a compared with that of the dianion of 3.
phenes or bithiophenes by Ni- or Pd-catalyzed Kumada Therefore, we decided to use an alternative synthetic strat-
cross-coupling or Cu-catalyzed oxidative homocoupling.[11] egy based on Suzuki–Miyaura coupling[14] as a key step. It
This approach provides fair-to-excellent yields but requires should be noted here that only limited examples of oligo-
a relatively high number of synthetic steps. The commercial thiophenes with different substituents in one molecule have
availability of terthiophene 3 and quaterthiophene 4 been reported. Funahashi and Hanna recently reported
prompted us to examine their direct one-step functionaliza- high charge-carrier mobility in smectic phases of α-alkyl-
tion to give 1 and 2.
αЈ-alkynyloligothiophenes prepared by multistep synthesis
Very recently, we reported in a preliminary communica- involving sequential Kumada couplings as key steps in as-
tion a practical and high-yield one-step synthesis of α,αЈ- sembling the oligothiophene core.[15] Although it appeared
bis(n-alkyl)oligothiophenes such as 1a,b and 2 by lithiation that nonsymmetrical oligothiophenes should be easily ac-
of 3 and 4, respectively, followed by alkylation with n-alkyl cessible by the Suzuki coupling of the corresponding build-
halides.[9] The use of tBuOK to enhance the reactivity of ing blocks, no successful attempts are mentioned in the lit-
dilithiated oligothiophene species towards alkylating agents erature. In addition, syntheses based on Suzuki coupling
was demonstrated to be of crucial importance. Without the appeared particularly practical because of the great and
addition of tBuOK, the reaction resulted in small amounts constantly increasing variety of commercially available aryl-
of mono- and disubstituted oligothiophenes, and up to 85% boronic reagents.
of unreacted starting material was recovered. Earlier, it was
The reaction between commercially available n-hexyl-
reported that the simple addition of tBuOK considerably substituted bithiophenylboronate 7 and 2-bromo-5-octyl-
enhanced the reactivity of various lithiated species, includ- thiophene (8) directly furnished the nonsymmetrical ter-
ing 2-lithiated derivatives of furan, thiophene, and N-substi- thiophene 9 (60%) with linear alkyl chains of different
tuted pyrroles, toward alkylating agents such as haloalkanes length. Alternatively, Suzuki coupling of 2-bromo-5-alkyl-
and epoxides.[12] The observed effect was attributed to the thiophene 8 with boronate 11 and that of 2-bromothio-
formation of an organopotassium compound, likely in equi- phene (12) with boronate 7 delivered monosubstituted 2-
librium with a lithium derivative. The higher reactivity of alkylterthiophenes 6a and 6b, respectively, in 47–50% yield.
the former towards alkyl halides is probably due to the The second alkyl substituents were introduced by alkylation
lower aggregation, whereas organolithium compounds are in the presence of nBuLi/tBuOK as described above
well known to form associates in solution.[13]
(Scheme 2). In all Suzuki couplings to give 6a,b or 9, minor
Using the same method, symmetrical dialkyl derivatives amounts (10% or less) of the quaterthiophenenes 4 or 10
of terthiophene with branched 3,7-dimethyloctyl (com- resulting from the homocoupling[16] of the corresponding
pound 1c) or 5-methylhexyl (compound 1d) substituents bithiophenylboronates 11 or 7, respectively, were obtained.
Scheme 1. Synthesis of symmetrical dialkyloligothiophenes 1a–d, 2, and 5.
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FULL PAPER
Scheme 2. Synthesis of nonsymmetrical dialkyloligothiophenes 9, 13, and 14.
Fortunately, these impurities were easy to separate by Table 1. Transition temperatures of dialkyloligothiophenes 1a–d, 2,
5, 9, 13, and 14.
taking advantage of the much lower solubility of the quater-
thiophenes relative to that of the terthiophenes.
En-
try
Com-
pound
Transition temperatures/°C
[enthalpy /kJmol–1][a,b]
1
1a[c]
Cr 62 [21.7] SmG 68 [3.2]
Thermotropic Behavior and Structure of Mesophases
SmF 84 [0.8] SmC 87 [6.8] I
Cr 48 [13.6] SmG 75 [11.3] I
Cr 45 [25.2] I
2
3
4
5
6
1b[c]
1c
1d
2[c]
5
Thermotropic properties of the novel oligothiophenes as
well as those of some previously synthesized symmetrical
oligothiophenes with linear alkyl substituents are summa-
rized in Table 1. Terthiophene 1c with two double-branched
3,7-dimethyloctyl substituents is a low-melting crystalline
solid that does not form liquid crystalline mesophases. The
melting point of 1c is much lower than the Cr–LC transi-
tion temperature of its straight-chain analog, dioctylter-
Cr 85 [13.7] I
Cr 77 [4.3] LC 140 [6.0] I
Cr 42 [1.5] (LC1 58 [3.9]) (LC2 65 [0.2])
LC3 127 [29.1] I
Cr 52 [15.6] LC 65 [7.1] I
Cr1 32 [4.3] Cr2 41 [0.7] Sm G/H 79 [19.2] I
Cr 20 [5.1] (LC1 33 [0.3]) LC2 43[5.5] I
7
8
9
9
13
14
[a] Determined from the onset of the second heating curve (DSC);
thiophene 1a (Table 1, entries 1 and 3). This is probably due Cr: crystalline phase; Sm: smectic phase; Sm G/H: smectic G or H
phase; LC: undefined liquid crystalline phase of unknown nature;
to both the conformational changes in the side chains and
I: isotropic liquid. [b] The transitions in brackets are monotropic
their stereoheterogeneity, as the synthesis of 1c from the
transitions (observed only during the heating). [c] Data from ref.[9]
racemic 1-bromo-3,7-dimethyloctane gave a mixture of two
are given for the sake of discussion.
diastereoisomers. However, because of the steric repulsion
of the bulkier peripheral substituents, the π–π stacking of
the cores is also disturbed. Accordingly, at the disordering alkyl substituents, must be explained by the more efficient
temperature of the side chains, the aromatic cores are al- π–π stacking between the longer quaterthiophene moieties.
ready unstacked, and the crystalline solid melts directly to Comparison of the thermotropic behavior of 1c and 5
the isotropic liquid. We reasoned that the thermotropic be- clearly demonstrates the importance of the well-adjusted
havior of 1d, which possesses less bulky 5-methylhexyl sub- balance between the stacking of the aromatic core and the
stituents and also lacks the center of chirality, may be an disorder caused by the peripheral alkyl chains.
average between those of 1a and 1c. Unfortunately, 1d does
Another approach to the tuning of thermotropic proper-
not form liquid crystalline phases either, and its melting ties involves the introduction of two different substituents
point is unexpectedly high relative to the Cr–LC transition at the oligothiophene core. Thus, the above-mentioned
temperature of its straight-chain analog 1b (Table 1, entries combination of n-alkyl and n-alkynyl substituents resulted
2 and 4).
in few examples of oligothiophenes that are liquid crystal-
Unlike those in terthiophene 1c, the two 3,7-dimethyloc- line at ambient temperature.[15] We studied the influence of
tyl substituents in quaterthiophene 5 stabilize the meso- two alkyl substituents that differ in length or in branching
phase, and the Cr–LC transition temperature is lowered by sites on the thermotropic behavior of oligothiophenes. Ter-
35 °C relative to that of the straight-chain dioctylquater- thiophene 9 with two linear alkyl substituents of different
thiophene 2 (Table 1, entries 5 and 6). Undoubtedly, the length (n-hexyl and n-octyl) has nearly the same Cr–LC
major difference in thermotropic behavior between quater- transition temperature as that of the symmetrical dihexyl
thiophene 5 and terthiophene 1c, both bearing identical analog 1b but a lower clearing point (Table 1, entries 2 and
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Symmetrical and Nonsymmetrical Liquid Crystalline Oligothiophenes
FULL PAPER
7). A more pronounced effect was observed when a zation (28.0 kJmol–1). It is, however, not possible to distin-
branched chain and a linear chain were combined in the guish between these two phases on the basis of our X-ray
same molecule. In the design of the nonsymmetrical ter- diffraction data.[20]
thiophenes 13 and 14, we kept the length of the two alkyl
substituents in the molecule the same but introduced ad-
ditional branching sites (methyl groups) in one of them. An
additional methyl substituent on one of the hexyl chains
of the nonsymmetrical molecule 13 essentially stabilizes the
mesophase: the temperature of the Cr–LC transition de-
creases relative to that of the symmetrical analog 1b, while
the clearing point remains nearly unchanged (Table 1, en-
tries 2 and 8). As expected, a bulkier 3,7-dimethyloctyl sub-
stituent in 14 causes more pronounced changes in the ther-
motropic behavior, and both the temperature of Cr–LC
transition and the isotropization point are remarkably
lower than those of dioctylterthiophene 1a (Table 1, entries
Figure 1. DSC curve of the nonsymmetrical terthiophene 13,
1 and 9). Notably, the nonsymmetrical terthiophene 14 is
10 °Cmin–1; Cr: crystalline phase, Sm G/H: smectic G or H phase,
I: isotropic liquid. Temperatures and enthalpies of the phase transi-
liquid crystalline at ambient temperature (between 23 and
49 °C). For all liquid crystalline mesophases of the oligo-
thiophenes, birefringent flowing textures were obtained by
polarized optical microscopy (POM) (see Supporting Infor-
mation).
tions are given in Table 1.
The supramolecular structure of the nonsymmetrical ter-
thiophene 13 has been studied in detail. We paid particular
attention to this compound because of its very low enthalpy
of transition between the LC and crystalline phases, which
could enable us to obtain also single-crystalline aligned
films for OFET applications.[17] At lower temperatures, two
different crystalline phases exist, and the transition between
them is at 32 °C (Figure 1). The mosaic texture (POM) of
the phase between 41 °C and 79 °C (clearing point) suggests
its smectic liquid crystalline nature.[18] This was corrobo-
rated by powder X-ray diffraction. The diffractogram of 13
at 65 °C displays an intense reflection at q = 0.26 Å–1 (Fig-
ure 2). This peak is indexed as (001) and corresponds to the
interplanar spacing (smectic layer thickness) of 24.3 Å.
From the comparison of the thickness of the smectic layer
with the length of the molecule (ca. 28 Å, estimated from
the AM1 molecular geometry optimization), it can be con-
cluded that the long axes of the molecules are tilted at ca.
30° relative to the normal of the smectic plane. Higher-
order reflection peaks are observed at q = 0.52 Å–1 (002),
0.78 Å–1 (003), and 1.03 Å–1 (004). They indicate long-range
order in the direction perpendicular to the smectic plane.
Peaks at q = 1.48 Å–1, 1.68 Å–1, and 1.90 Å–1 are indexed
as (020), (110), and (–120), respectively, and correspond to
interplanar distances. Peaks at q = 1.31 Å–1 and 1.38 Å–1
are assigned to intermolecular distances between the sulfur
atoms (4.80 Å and 4.57 Å, respectively).[1,19] The reflections
at high q values arises from the packing of the molecules
within the smectic layers. A hexatic structure and a mono-
clinic cell are derived with the following calculated param-
eters: a = 4.60 Å, b = 8.54 Å, c = 24.3 Å, γ = 96°. Together,
the tilt of the long axis of molecules relative to the normal
of the smectic plane and the reflections at high q values are
consistent with a highly ordered smectic G or H phase. This
conclusion is supported by the low enthalpy of the Cr2–Sm
Figure 2. X-ray diffractogram of 13 at 65 °C; S–S is used for dis-
tances between sulfur atoms.
Conclusions
We have described a practical synthesis of symmetrical
and nonsymmetrical terthiophenes and quaterthiophenes
involving Suzuki coupling and carbanion alkylation as key
steps. The branching of the side chains and desymmetriz-
ation of the molecule are two efficient tools for tailoring
thermotropic properties of rodlike mesogens. A balance be-
tween the order caused by the stacking of the aromatic
cores and the disorder caused by the alkyl chains should be
carefully optimized to obtain desirable thermotropic prop-
erties. Using different approaches, we achieved a wide me-
sophase temperature range and liquid crystallinity at room
temperature, two important properties for the fabrication of
organic semiconducting devices. Studies of the performance
of novel liquid crystalline oligothiophenes in field-effect
transistors are in progress.
Experimental Section
General: All chemicals were purchased from Aldrich or Acros and
transition (1.0 kJmol–1) and the high enthalpy of isotropi- used without further purification unless stated otherwise. THF was
Eur. J. Org. Chem. 2007, 1256–1261
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J. Leroy, N. Boucher, S. Sergeyev, M. Sferrazza, Y. H. Geerts
FULL PAPER
refluxed over sodium and benzophenone until a blue-violet color
persisted, and it was distilled directly into the reaction flask. A
commercially available solution of nBuLi in hexane was titrated
with Ph2CHCOOH immediately before use. tBuOK was used as a
1- solution in THF. Dialkyloligothiophenes 1a, 1b, and 2 were
synthesized as described by us earlier.[9] 1-Iodo-5-methylhexane was
prepared by the Finkelstein reaction: a mixture of 1-bromo-5-meth-
ylhexane (1 mmol) and NaI (1.5 mmol) in acetone (10 mL) was
heated at reflux overnight; after filtration and careful evaporation
pure 1d. Yellow solid; yield 0.847 g (90%); m.p. 85 °C. 1H NMR
(300 MHz, CDCl3, 25 °C): δ = 6.97 (s, 2 H), 6.96 (d, J = 4.5 Hz, 2
H), 6.68 (d, J = 3.5 Hz, 2 H), 2.80 (t, J = 7.5 Hz, 4 H), 1.67 (quint,
J = 7.5 Hz, 4 H), 1.50–1.58 (m, 2 H), 1.36–1.50 (m, 4 H), 1.20–
1.30 (m, 4 H), 0.88 (d, J = 7 Hz, 12 H) ppm. 13C NMR (75 MHz,
CDCl3, 25 °C): δ = 145.4, 136.1, 134.6, 124.8, 123.4, 123.2, 38.7,
31.8, 30.2, 27.9, 26.9, 22.6 ppm. HR-EI-MS: calcd. for C26H36S3
[M]+ 444.1979; found 444.1968.
(؎)-(S,S/R,R)-
and
meso-5,5ЈЈЈ-Bis(3,7-dimethyloctyl)-
1
of the solvent, the crude product (judged to be Ͼ95% pure by H
2,2Ј:5Ј,2ЈЈ:5ЈЈ,2ЈЈЈ-quaterthiophene (5), Mixture of Diastereoisomers:
Prepared according to General Procedure 1 with the following
amendment: quaterthiophene 4 (500 mg, 1.5 mmol) was dissolved
in dry THF (50 mL) and treated with nBuLi (4.5 mmol), tBuOK
NMR) was used without further purification. 2-Bromo-5-octylthio-
phene (8) was synthesized according to a published procedure.[21]
Column chromatography: SiO2 Kieselgel 60 (Macherey–Nagel,
particle size 0.04–0.063 mm). TLC: precoated SiO2 plates Kieselgel
60F254 (Merck). 1H NMR (300 MHz) and 13C NMR (75 MHz)
spectra were recorded in CDCl3 with a Bruker Avance 300 spec-
trometer; chemical shifts (δ) are given in ppm relative to Me4Si
(internal standard); coupling constants (J) are given in Hz. EI-MS
(70 eV) spectra were recorded with a VG Micromass 7070F instru-
ment. Phase transition temperatures were measured by differential
scanning spectroscopy (Mettler Toledo DSC 821) at heating and
cooling rates of 10 °Cmin–1. Optical textures of mesophases were
observed with a polarizing microscope (Nikon Eclipse 80i). Powder
X-ray diffraction measurements were carried out with a Bruker D8-
diffractometer (Cu-Kα radiation).
(6 mmol),
and
(Ϯ)-1-bromo-3,7-methyloctane
(3.75 mmol,
0.78 mL). Column chromatography (hexane/toluene 90:10) af-
forded analytically pure 5. Yellow solid; yield 0.778 g (85%). 1H
NMR (300 MHz, CDCl3, 25 °C): δ = 6.99–7.07 (m, 6 H), 6.71 (d,
J = 3.4 Hz, 2 H), 2.70–2.90 (m, 4 H), 1.65–1.75 (m, 2 H), 1.07–
1.55 (m, 18 H), 0.93 (d, J = 6.2 Hz, 6 H), 0.87 (d, J = 8.1, 12 H)
ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 145.9, 136.7, 135.4,
134.4, 124.7, 124.0, 123.5, 123.4, 39.3, 38.9, 37.0, 32.3, 27.9, 27.8,
24.7, 22.7, 22.6, 19.5 ppm. HR-EI-MS: calcd. for C36H50S4 [M]+
610.2801; found 610.2795.
5-Octyl-2,2Ј:5Ј,2ЈЈ-terthiophene (6a): Prepared according to Gene-
ral Procedure 2 from boronate 11 (1.17 g, 3.0 mmol) and bromide
8 (540 mg, 2.0 mmol). Column chromatography (hexane) followed
by crystallization from methanol/toluene afforded analytically pure
6a. Yellow solid; yield 0.360 g (50%); m.p. 69 °C. 1H NMR
(300 MHz, CDCl3, 25 °C): δ = 7.20 (dd, J = 5.1, 1.1 Hz, 1 H),7.17
(dd, J = 3.6, 1.1 Hz, 1 H), 7.05 (d, J = 3.6 Hz, 1 H), 6.99–7.03 (m,
3 H), 6.68 (d, J = 3.6 Hz, 1 H), 2.79 (t, J = 7.5 Hz, 2 H), 1.68
(quint, J = 7.5 Hz, 2 H), 1.27–1.44 (m, 10 H), 0.88 (t, J = 6.6 Hz,
3 H) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 145.6, 137.3,
136.8, 135.5, 134.4, 127.8, 124.8, 124.3, 124.2, 123.5, 123.4, 31.9,
31.6, 30.2, 29.3, 29.2, 29.1, 22.7, 14.1 ppm (1 signal of aromatic C
is missing due to overlap). HR-EI-MS: calcd. for C20H24S3 [M]+
360.1040; found 360.1025.
General Procedure 1: Alkylation of 2,2Ј:5Ј,2ЈЈ-Terthiophene (3): A
solution of terthiophene 3 (500 mg, 2.12 mmol) in dry THF
(10 mL) was cooled to –78 °C, and a solution of nBuLi (ca. 1.6  in
hexane, 6.04 mmol) was added dropwise by cannula. The reaction
mixture was stirred for 10 min at –78 °C, then a solution of tBuOK
(1.0  in THF, 8.05 mmol) was added. The stirring was continued
for 15 min at –78 °C, then the 1-haloalkane (5 mmol) was added.
The reaction mixture was allowed to slowly reach room tempera-
ture, stirred overnight, quenched by the slow addition of water
(10 mL), and extracted with hexane (3ϫ10 mL). After evaporation
of the solvent, the residue was purified by column chromatography
or crystallized from methanol/toluene to give pure 1.
General Procedure 2: Synthesis of Terthiophenes 6 and 9 by Suzuki
Coupling: A suspension of pinacolborane ester 7 or 11 (7.5 mmol)
in EtOH (10 mL) and a solution of K2CO3 (3.43 g, 24.8 mmol) in
H2O (15 mL) were added to a solution of bromide 8 or 12
(5.0 mmol) and [Pd(PPh3)4] (61 mg, 0.05 mmol) in toluene
(100 mL). The mixture was heated at 75 °C for 45 min, then cooled
to room temperature and diluted with hexane (100 mL). The or-
ganic layer was dried with MgSO4 and concentrated in vacuo. The
residue was purified by column chromatography to give pure 6 or
9.
5-Hexyl-2,2Ј:5Ј,2ЈЈ-terthiophene (6b): Prepared according to Gene-
ral Procedure 2 from boronate 7 (1.00 g, 3.0 mmol) and bromide
12 (0.2 mL, 2.0 mmol). Column chromatography (hexane) followed
by crystallization from methanol/toluene afforded analytically pure
6b. Yellow solid; yield 0.312 g (47%); m.p. 57 °C. 1H NMR
(300 MHz, CDCl3, 25 °C): δ = 7.20 (dd, J = 5.1, 1.1 Hz, 1 H), 7.15
(dd, J = 3.3, 1.1 Hz, 1 H), 7.06 (d, J = 3.6 Hz, 1 H), 6.98–7.03 (m,
3 H), 6.69 (d, J = 3.6 Hz, 1 H), 2.80 (t, J = 7.5 Hz, 2 H), 1.69
(quint, J = 7.5 Hz, 2 H), 1.27–1.44 (m, 6 H), 0.90 (t, J = 6.6 Hz, 3
H) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 145.6, 137.3,
136.8, 135.5, 134.4, 127.8, 124.8, 124.3, 123.5, 123.4, 31.6 (2C),
30.2, 28.7, 22.6, 14.1 ppm (2 signals of aromatic C are missing due
to overlap). HR-EI-MS: calcd. for C18H20S3 [M]+ 332.0727; found
332.0711.
(؎)-(S,S/R,R)- and meso-5,5ЈЈ-Bis(3,7-dimethyloctyl)-2,2Ј:5Ј,2ЈЈ-ter-
thiophene (1c), Mixture of Diastereoisomers: Prepared according to
General Procedure
1
from (Ϯ)-1-bromo-3,7-dimethyloctane
(0.860 mL). Crystallization from methanol/toluene afforded pure
1c. Yellow solid; yield 0.986 g (88%); m.p. 45 °C. 1H NMR
(300 MHz, CDCl3, 25 °C): δ = 6.96 (s, 2 H), 6.95 (d, J = 3.6 Hz, 2
H), 6.67 (d, J = 3.6 Hz, 2 H), 2.70–2.90 (m, 4 H), 1.63–1.72 (m, 2
H), 1.44–1.56 (m, 4 H), 1.08–1.35 (m, 14 H), 0.92 (d, J = 2.5 Hz,
6 H), 0.88 (d, J = 2.5 Hz, 12 H) ppm. 13C NMR (75 MHz, CDCl3,
25 °C): δ = 145.6, 136.1, 134.6, 124.6, 123.4, 123.1, 39.3, 38.7, 37.0,
32.3, 27.9, 27.8, 24.7, 22.7, 22.6, 19.5 ppm. HR-EI-MS: calcd. for
C32H48S3 [M]+ 528.2918; found 528.2919.
5-Hexyl-5ЈЈ-octyl-2,2Ј:5Ј,2ЈЈ-terthiophene (9): Prepared according to
General Procedure 2 from boronate 7 (1.03 g, 2.8 mmol) and bro-
mide 8 (500 mg, 1.82 mmol). Crystallization from methanol/tolu-
1
ene gave analytically pure 9. Yellow solid; yield 0.485 g (60%). H
NMR (300 MHz, CDCl3, 25 °C): δ = 6.96 (s, 2 H),6.95 (d, J =
4.1 Hz, 2 H), 6.67 (d, J = 4.1 Hz, 2 H), 2.78 (t, J = 7.5 Hz, 4 H),
1.68 (quint, J = 7.5 Hz, 4 H), 1.28–1.40 (m, 16 H), 0.86–0.92 (m,
6 H) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 145.4, 136.1,
134.6, 124.7, 123.4, 123.1, 31.8, 31.6, 31.5, 30.2, 29.3, 29.2, 29.1,
28.7, 22.6, 22.5, 14.1, 14.0 ppm (2 signals of aliphatic C are missing
5,5ЈЈ-Bis(5-methylhexyl)-2,2Ј:5Ј,2ЈЈ-terthiophene (1d): Prepared ac-
cording to General Procedure 1 from 1-iodo-5-methylhexane
(1.13 g). Column chromatography (hexane) afforded analytically
1260
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Eur. J. Org. Chem. 2007, 1256–1261

Symmetrical and Nonsymmetrical Liquid Crystalline Oligothiophenes
FULL PAPER
due to overlap). HR-EI-MS: calcd. for C26H36S3 [M]+ 444.1979;
found 444.1998.
project). We thank Dr. Matthias Lehmann (University of Chem-
nitz, Germany) for discussions.
5-Hexyl-5ЈЈ-(5-methylhexyl)-2,2Ј:5Ј,2ЈЈ-terthiophene (13): Prepared
according to General Procedure 1 with the following amendment:
5-hexylterthiophene 6b (250 mg, 0.75 mmol) was dissolved in THF
(10 mL) and treated with nBuLi (1.1 mmol), tBuOK (1.5 mmol),
and 1-iodo-5-methylhexane (0.25 mL, 1.5 mmol). Column
chromatography (hexane/toluene, 9:1) followed by crystallization
from methanol/toluene afforded analytically pure 13. Yellow solid;
[1] D. Fichou, J. Mater. Chem. 2000, 10, 571–588.
[2] G. Horowitz, Adv. Mater. 1998, 10, 365–377.
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Liq. Cryst. 1995, 265, 61–76.
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323.
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2000, 346, 183–192.
1
yield 0.194 g (60%). H NMR (300 MHz, CDCl3, 25 °C): δ = 6.96
(s, 2 H), 6.95 (d, J = 4.1 Hz, 2 H), 6.67 (d, J = 4.1 Hz, 2 H), 2.78
(t, J = 7.5 Hz, 4 H), 1.22–1.77 (m, 15 H), 0.88–0.96 (m, 9 H) ppm.
13C NMR (75 MHz, CDCl3, 25 °C): δ = 145.4, 136.1, 134.6, 124.7,
123.4, 123.2, 38.7, 31.8, 31.6, 30.2, 30.2, 28.7, 27.9, 26.9, 22.6, 22.5,
14.1 ppm (2 signals of aliphatic C are missing due to overlap). HR-
EI-MS: calcd. for C25H34S3 [M]+ 430.1823; found 430.1819.
[7] M. Funahashi, J. Hanna, Appl. Phys. Lett. 2000, 76, 2574–
2576.
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8583.
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166–167.
(؎)-5-(3,7-Dimethyloctyl)-5ЈЈ-octyl-2,2Ј:5Ј,2ЈЈ-terthiophene
(14):
[10] M. Kastler, W. Pisula, D. Wasserfallen, T. Pakula, K. Müllen,
J. Am. Chem. Soc. 2005, 127, 4286–4296.
Prepared according to General Procedure 1 with the following
amendment: 5-octylterthiophene 6a (250 mg, 0.69 mmol) was dis-
solved in THF (10 mL) and treated with nBuLi (1.05 mmol),
[11] S. Ponomarenko, S. Kirchmeyer, J. Mater. Chem. 2003, 13,
197–202.
[12] L. Brandsma, A. G. MalЈkina, L. Lochmann, P. von Schleyer,
Trav. Chim. Pays Bas 1994, 113, 529–530.
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C. M. P. Kronenburg, N. Krause, G. van Koten, Angew. Chem.
Int. Ed. Engl. 1997, 36, 755–757; c) W. Bauer, D. Seebach, Helv.
Chim. Acta 1984, 67, 1972–1988.
tBuOK
(1.4 mmol),
and
(Ϯ)-1-bromo-3,7-dimethyloctane
(0.22 mL, 1.4 mmol). Column chromatography (hexane/toluene,
9:1) followed by crystallization from methanol/toluene afforded an-
alytically pure 14. Yellow solid; yield 0.207 g (60%). 1H NMR
(300 MHz, CDCl3, 25 °C): δ = 6.96 (s, 2 H),6.95 (d, J = 4.1 Hz, 2
H), 6.67 (d, J = 4.1 Hz, 2 H), 2.78 (t, J = 7.5 Hz, 4 H), 1.10–1.80
(m, 22 H), 0.80–0.96 (m, 12 H) ppm. 13C NMR (75 MHz, CDCl3,
25 °C): δ = 145.4, 145.6, 136.1, 134.6, 134.6, 124.8, 124.6, 123.4,
123.1, 39.3, 38.9, 37.0, 32.3, 31.8, 31.6, 30.2, 29.3, 29.2, 29.1, 27.9,
27.8, 24.7, 22.7, 22.6, 19.5, 14.1 ppm (3 signals of aromatic C are
missing due to overlap). HR-EI-MS: calcd. for C30H44S3 [M]+
500.2605; found 500.2613.
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7508–7510.
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de Leeuw, A. J. J. M. van Breemen, R. Resel, Adv. Mater. 2006,
18, 896–899.
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Weinheim, 2003.
[19] H. Zhang, S. Shiino, A. Kanazava, O. Tsutsumi, T. Shiono, T.
Ikeda, Y. Nagase, Synth. Met. 2002, 126, 11–18.
[20] P. Oswald, P. Pieranski, Les cristaux liquides, Vol. 1, Gordon
and Breach, Paris, 2000.
Supporting Information (see footnote on the first page of this arti-
cle): POM textures of 5, 9, 13, and 14; powder X-ray diffraction
data of 13.
Acknowledgments
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8064.
We gratefully acknowledge financial support of this study from the
Government of the Walloon Region (ETIQUEL project) and the
Belgian National Science Foundation (FNRS, FRFC 2.4608.04
Received: September 28, 2006
Published Online: January 17, 2007
Eur. J. Org. Chem. 2007, 1256–1261
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1261