Low temperature enantiotropic nematic phases from V-shaped, shape-persistent molecules

Article abstract of DOI:10.3762/bjoc.5.73

A series of V-shaped, shape-persistent thiadiazole nematogens, based on an oligo(phenylene ethynylene) scaffold with ester groups connected via alkyloxy spacers, was efficiently prepared by a two-step procedure. Phase engineering results in an optimum of

Full text of DOI:10.3762/bjoc.5.73

Low temperature enantiotropic nematic phases from
V-shaped, shape-persistent molecules
Matthias Lehmann* and Jens Seltmann
Full Research Paper
Open Access
Address:
Beilstein Journal of Organic Chemistry 2009, 5, No. 73.
Institute of Chemistry, Chemnitz University of Technology, Straße der
Nationen 62, 09111 Chemnitz, Germany
doi:10.3762/bjoc.5.73
Received: 22 July 2009
Email:
Accepted: 17 November 2009
Published: 04 December 2009
Matthias Lehmann* - Matthias.Lehmann@chemie.tu-chemnitz.de
* Corresponding author
Guest Editor: S. Laschat
Keywords:
© 2009 Lehmann and Seltmann; licensee Beilstein-Institut.
License and terms: see end of document.
biaxial nematics; liquid crystals; phase engineering; thiadiazoles;
V-shaped mesogens
Abstract
A series of V-shaped, shape-persistent thiadiazole nematogens, based on an oligo(phenylene ethynylene) scaffold with ester groups
connected via alkyloxy spacers, was efficiently prepared by a two-step procedure. Phase engineering results in an optimum of the
mesophase range and low melting temperature when the nematogens are desymmetrised with a butoxy and a heptyloxy spacer. The
mesophases are enantiotropic and over the whole temperature range nematic. For the optimised mesogen structure, optical investi-
gations by conoscopy monitored a uniaxial nematic phase upon cooling from the isotropic phase to room temperature (ΔT = 150
°C). X-ray studies on magnetic-field-aligned samples of this mesogen family revealed a general pattern, indicating the alignment of
two molecular axes along individual directors in the magnetic field. These observations may be rationalised with larger assemblies
of V-shaped molecules isotropically distributed around the direction of the magnetic field.
Introduction
Most molecules forming nematic liquid crystals, the nemato- nematogens in theoretical studies has been simplified to a
gens, are based on rod-shaped (calamitic), anisometric cores spherocylinder [3]. These phases are called uniaxial. Almost 40
with peripheral flexible chains along the molecular long axis years ago, M. J. Freiser predicted that real nematogens possess
[1]. Nematic phases are the simplest liquid crystalline meso- a non-cylindrical shape and thus should be able to form biaxial
phases, in which phase anisotropy of crystals is combined with nematic phases at an appropriate low temperature [4]. What is a
fluid properties of liquids. In the nematic phases of calamitic biaxial nematic phase and why is it so interesting? Uniaxial and
mesogens only the molecular long axes are oriented along a so biaxial phases can be best understood by the property from
called director [2] and the molecular centres of gravity are which this classification originates: the behaviour when light
distributed like in a liquid. In models, the molecules are thought propagates in the material. The optical property of a uniaxial
to turn rapidly about their long axis and therefore the shape of phase in a monodomain can be described by two refractive
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Beilstein Journal of Organic Chemistry 2009, 5, No. 73.
indices spanning a rotationally symmetric ellipsoid, also called troscopy [8-10]. This has been recently confirmed by various
indicatrix (Figure 1, left side). There is one particular direction, other methods [11-14]. Since then several new materials have
perpendicular to the circular cross section of this special been designed and reported to be biaxial, among others tetra-
ellipsoid, along which the propagating linear polarised light podes [15-17] and banana-shaped oligoesters [18,19]. However,
does not change its polarisation. This direction is called the there is still a controversial discussion about the phase biaxi-
optical axis. In a uniaxial phase there is only one optical axis. ality of these materials and their switching behaviour [20-22].
However, if the monodomains of materials have to be optically All these latter molecular structures are, however, flexible and
described with three different refractive indices, the indicatrix is can change their conformation and thus their shape. Since theor-
an ellipsoid spanned by three different semi-principal axes, etically biaxial nematic phases were predicted for a molecule
possessing two different circular cross sections and with a defined shape and angle, we aimed to design a shape-
consequently two optical axes (Figure 1, right side). persistent molecular scaffold of type I (Figure 2) based on
oligo(phenylene ethynylene) building blocks. These molecules
In a biaxial nematic phase three molecular axes align along show liquid crystal behaviour only with a flat bending unit
individual directors resulting in a material with three different possessing a dipole along the apex of the mesogen, sufficiently
refractive indices. However, at the same time this material has a long aliphatic chains R and at least one pyridyl or acceptor
liquid-like distribution of the molecular centres of gravity. In substituted aromatic unit at the periphery of the molecule [23,
spite of the high molecular mobility the high order should be 24]. Fluorenone [25], oxadiazole [26], thiazole and thiadiazole
maintained. These two parameters have to be balanced [24] derivatives have been synthesised and evidence for biaxi-
extremely precise in order to obtain a thermotropic biaxial ality in their monotropic nematic phases has been presented.
nematic with molecules of low molar mass [5].
Monotropic phases are metastable and crystallise, thus making
detailed studies of these phases extremely difficult. Therefore,
Historically, a biaxial nematic phase was found first in lyotropic low temperature stable (enantiotropic) phases are urgently
mixtures, where the micellar shape can be gradually tuned [6]. demanded. In an earlier theoretical work, weak hydrogen bonds
A thermotropic biaxial nematic phase of molecules of low were suggested to possibly induce and stabilise biaxial nematic
molar mass is in high demand because of its potential applica- phases [27]. Therefore, we modified our design concept and at-
tion in display technology. After the discovery of the biaxial tached ester groups to the peripheral aromatic unit via an
nematic phase in lyotropic materials, many claims of biaxial alkyloxy spacer to obtain the general structures of type II. The
thermotropic nematic phases were published without being esters may be subsequently cleaved, in order to generate
accepted [5]. During this period also banana-shaped molecules carboxylic acids and thus hydrogen bonded dimers and
were discovered and theoreticians highlighted the possibility to oligomers. In this article, the synthesis of a series of
use bent-shaped molecules with rigorously defined shape thiadiazoles of general structure II is presented and the
(bending angle) for the formation of the desired phase [5,7]. But successful approach to low temperature, enantiotropic nematic
it was not until 2004 that sufficient evidence was presented for liquid crystals in the family of bent-shaped oligo(phenylene
biaxiality of nematic phases in the series of V-shaped ethynylenes) will be discussed.
oxadiazoles by X-ray diffraction and solid-state 2H NMR spec-
Figure 1: Uniaxial nematic (left) and biaxial nematic (right) phases and their corresponding indicatrices.
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Beilstein Journal of Organic Chemistry 2009, 5, No. 73.
Figure 2: Design of V-shaped, shape-persistent oligo(phenylene ethynylene) mesogens of type I and II (R, R′ = alkyl chains; n, m = 4–10).
Results and Discussion
(Scheme 2) [24]. All compounds were carefully purified and
Synthesis
characterised by 1H, 13C NMR, mass spectrometry and
The shape-persistent arms of the new nematogens were elemental analysis (see experimental section).
prepared following the recent optimised procedure [25], using
the mono-protected diethynylbenzene derivative 4 as a key Thermotropic Properties
compound (Scheme 1). The peripheral aromatic units 5 were The thermotropic behaviour of all materials was investigated by
obtained by etherification of 4-iodophenol with the correspond- differential scanning calorimetry (DSC) and polarised optical
ing ethyl ω-bromoalkanoate [28]. Cross-coupling of iodoben- microscopy (POM). The results are collected in Table 1. Inter-
zene 5 with ethynyl compound 4 and subsequent cleavage of the estingly, all phenylene ethynylene oligomers show exclusively
silyl protecting group afforded the arm derivatives 6. As in the enantiotropic nematic liquid crystal phases, even for the hockey
previously published two-step synthesis, the arms 6 were linked stick shaped intermediates 3. However, the temperature inter-
successively to the non-symmetric thiadiazole bending unit 7 vals for the latter are small, approaching a maximum of 43 °C
Scheme 1: Synthesis of arm derivatives 6. Reaction conditions: (i) 1) Pd(PPh3)4, CuI, piperidine, rt; 2) TBAF, THF, rt.
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Beilstein Journal of Organic Chemistry 2009, 5, No. 73.
Scheme 2: Two-step synthesis of V-shaped nematogens: symmetric (1) and non-C2-symmetric (2) thiadiazoles. Reaction conditions: (i) Pd(PPh3)4,
CuI, piperidine, rt; (ii) Pd(PPh3)4, CuI, piperidine, 65 °C.
for compound 3c and melting in all cases occurs only above
100 °C (Figure 3). In this series, an odd-even behaviour
becomes apparent for the Cr–N, as well as for the N–I trans-
ition with increasing chain length (n = 4–7) [1,29]. It is
important to note that for the first three members (3a–c) there is
only a small impact of the chain length on the phase transition
temperatures. Only with the heptyl chains do the transition tem-
peratures decrease significantly. A closer look at transition
enthalpies and entropies reveal very small values for 3a and 3b
(ΔH = 0.1 kJ·mol−1; ΔS = 0.2 J·K−1·mol−1). Entropy values
approaching zero, i.e. second order transitions, are predited for
direct transitions from the isotropic liquid to the biaxial nematic
phase for biaxial molecules [30]. Thus, these hockey stick
shaped derivatives may be good candidates for the investiga-
Figure 3: Comparison of the mesophase ranges of intermediate
hockey stick compounds 3 and symmetric V-shaped nematogens 1.
tion of the presence of phase biaxiality. POM studies reveal for
derivatives 3a–e Schlieren textures with two and four brushed
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Beilstein Journal of Organic Chemistry 2009, 5, No. 73.
illustrated in Figure 4. Apparently, the clearing temperature
decreases with the total number of peripheral methylene groups
(from 179.1 °C for 1a to 155.2 °C for 1e). Note that non-
symmetric compounds always possess lower melting and higher
clearing temperatures compared to their symmetric counter-
parts with the same number of methylene groups (compare 1b/
2b and 1d/2f). It appears that a large difference in chain lengths
results in higher stability of the mesophase, i.e. a low crystal-
lisation tendency (see 2f, 2g, 2b and 2c and compare to 2d and
2a). Maximum LC temperature intervals for enantiotropic liquid
crystalline phases of 109 °C and 108 °C were found for 2b and
2c, showing the success of the strategy for this series of com-
pounds. Note, as indicated in Table 1, that some of the samples
can be supercooled without crystallisation. Some materials can
be stored for more than 1 h at 25 °C without visible formation
of crystal grains.
Table 1: Thermotropic behaviour of hockey stick compounds 3 and
V-shaped molecules 1 and 2.
Compound
Rate 10 °C/min
ΔSN
(Onset [°C] / ΔH [kJ/mol])a
[J·mol−1·K−1]
3a
3b
3c
3d
3e
1a
1b
1c
1d
1e
2a
2b
2c
2d
2e
2f
Cr 126 / 35.1 N 159 / 0.1 I
Cr 120 / 44.0 N 158 / 0.1 I
Cr 119 / 47.0 N 162 / 0.9 I
Cr 112 / 42.6 N 141 / 1.4 I
Cr 118 / 58.0 N 150 / 0.9 I
Cr 96 / 65.9 N 179 / 1.8 I
Cr 91 / 55.6 N 171 / 1.6 I
Cr 99 / 56.5 N 174 / 1.8 I
Cr 108 / 57.6 N 164 / 1.9 I
Cr 108 / 117.7 N 155 / 1.8 I
Cr 88 / 102.3 N 179 / 1.9 I
Cr 68 / 38.5b N 178 / 1.9 I
Cr 67 / 37.0b N 175 / 1.8 I
Cr 89 / 48.3 N 175 / 1.7 I
Cr 96 / 55.5 N 171 / 1.8 I
Cr 70 / 37.3b N 168 / 1.7 I
Cr 77 / 53.6b N 162 / 1.7 I
0.2
0.2
2.1
3.4
2.1
4.0
3.6
4.0
4.4
4.2
4.2
4.2
4.0
3.8
4.1
3.9
3.9
2g
aData are given for the second heating.
bData for the first heating.
disclinations. Homeotropic alignment to study possible biaxi-
ality of the samples was not obtained. Only for a sample of
compound 3a could planar aligned thin LC films be prepared.
Upon rotation of the sample the film became alternately dark at
0° and birefringent at 45°.
Figure 3 compares the transitions of symmetric V-shaped com-
pounds 1a–e. The transition temperatures I–N decrease from
compounds with a short peripheral spacer between the aromatic
and the ester group to long spacer derivatives. A clear odd-even
effect is revealed. The transition enthalpies and entropies are
Figure 4: Comparison of the thermal behaviour of symmetric and non-
symmetric V-shaped molecules. The molecules are ordered from the
bottom to the top by increasing total number of spacer CH2 groups
(n + m).
relatively high (ΔH = 1.6–1.9 kJ·mol−1; ΔS = 3.6–4.2 Microscopy studies were performed to examine the nature of
J·K−1·mol−1) pointing to first order transitions. Melting tem- the mesophases. POM revealed for all samples Schlieren
peratures and melting enthalpies follow a different progression; textures with two and four brushed disclinations (Figure 5)
they decrease from 1a to 1b and increase again from 1b to 1e. typically observed for nematic phases. The high mobility of the
All melting temperatures are relatively high (above 90 °C). In phases, combined with a blaze of colours upon external pres-
order to lower the latter, non-symmetric V-shaped mesogens 2 sure and the absence of homeotropic alignment after shearing, is
with two arms consisting of different peripheral building blocks also a sign of their nematic nature. The nematic materials
have been prepared. The series of molecules 2a–c, 2f with a aligned preferentially planar on conventional glass substrates
pentanoic acid ethyl ester group on one side shows a decrease in and between glass coated with antiparallel rubbed polyimide
melting and clearing temperatures with increasing spacer alignment layers. Rotation of the samples exhibited alternately
lengths on the other arm. The decrease of melting temperature birefringent and dark textures. Conoscopy switched between a
dominates and reaches a minimum for molecule 2c with an blurry conoscopic cross and birefringent photographs. However,
octanoic acid ethyl ester as a peripheral group. In this series of the circular polariser could not reveal any optical axes. These
molecules no apparent odd-even effect can be monitored. The results would be expected for uniaxial as well as biaxial nematic
thermotropic properties in comparison with the increasing phases with planar alignment. Only homeotropic aligned
lengths of the peripheral alkanoic acid ethyl ester spacers are samples allow distinction between uniaxial and biaxial phases.
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Beilstein Journal of Organic Chemistry 2009, 5, No. 73.
In the case of 2c small homeotropically aligned areas could be Reflections (ii) correspond to a distance which can be rational-
obtained on glass substrates. Conoscopy revealed positive ised by the separation of two antiparallel thiadiazole rings along
optical anisotropy, thus the molecules’ long axes are aligned the molecular long axis. Reflections (iii) are typical for the π–π
perpendicular to the glass substrate. The black texture between distance between conjugated molecules. Note that for reflec-
the crossed polarisers at all rotation angles of the sample indi- tions (i) and (iii) the reflection conditions cannot be simultan-
cates the uniaxial nature right after the phase transition, further eously fulfilled. This points to the fact that at least two distinct
confirmed by the conoscopic cross. Upon cooling, the sample domains are observed by the experiment [31,32].
becomes slightly birefringent in some areas. This process
yielded an inhomogenous texture pointing to the formation of Table 2 summarises the Bragg distances d together with the
multiple small domains. The domains which remained dark correlation lengths ξ/d obtained by the Scherrer formula [33,
revealed a conoscopic cross at all temperatures. The symmetry 34]. It reveals that the values d(i–iv) are not a function of the
of the cross changed only slightly upon rotation of the sample. spacer lengths between peripheral aromatic units and the ester
These observations are in good agreement with the uniaxial groups. For example d(i) distances are almost constant in the
nature of the nematic phase of nematogen 2c even at room tem- range of 15–16 Å although the molecular length increases by 12
perature.
CH2 units from compound 1a to 1e. Even the distances d(ii),
attributed to the molecular long axis, on which the different
spacer length should have the largest impact, remain constant
between 9 and 10 Å. The latter can be rationalised when the
electron-poor thiadiazole units interact with the electron-rich
2,5-dialkyloxybenzenes of an antiparallel aligned mesogen. As
illustrated in Figure 6B, the sulfur atoms are then separated
throughout the sample on average by 9–10 Å. The fact that with
small angle X-ray scattering no reflection corresponding to the
overall molecular length could be found is not fully understood.
The correlation lengths ξ/d are all in the range of 3–5 repeating
units indicating the absence of any long range positional order
and thus confirming the nematic nature of the mesophases. The
π–π-distances are relatively large and only marginally smaller
than the average separation of alkyl chains. However, at this
temperature range similar values have been obtained previously
in the series of fluorenone derivatives, in which the π–π interac-
tion increased with decreasing temperature and moderated the
uniaxial to biaxial transition [25].
X-ray diffraction shows the orientation of two molecular axes in
this mesogen family, which may be an indication for phase
biaxiality. In contrast, the optical experiments of compound 2c
point to the uniaxial nature of its nematic phase. In order to
rationalise these two different results, it can be assumed on the
bases of the correlation lengths that the thiadiazoles form small
aggregates. These aggregates are responsible for the observed
diffuse X-ray pattern, however, they either rotate about their
long axis or the two different axes of the aggregates are isotro-
pically distributed around the direction of the magnetic field,
Figure 5: Textures of the nematic phase of 2c. a) Schlieren texture at
173 °C. b) and c) Planar alignment on rubbed polyimide at 167 °C (R =
rubbing direction). d) Homeotropic aligned area of 2c on glass at
163 °C. e) Conoscopic picture at 161 °C and f) Conoscopic picture
using the circular polariser.
X-ray Diffraction
X-ray studies were performed on magnetic-field-aligned eventually resulting in a uniaxial phase even at room tempera-
samples with the X-ray beam perpendicular to the alignment ture. The latter model has been recently suggested by a theor-
direction. Figure 6A shows a typical X-ray pattern found for all etical work from Vanakaras [35], in which three different
investigated derivatives with three diffuse pairs of reflections uniaxial and biaxial nematic phases based on aggregates or
(i–iii) and a halo (iv) corresponding to the average separation of clusters have been proposed. The model is further supported by
the liquid-like chains. As shown in Figure 6B, reflections (i) are results obtained from a bent-shaped oxazole derivative, which
assigned to the separation of the molecules along the bisector. forms polar clusters in the nematic phase [36]. However, further
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Beilstein Journal of Organic Chemistry 2009, 5, No. 73.
Figure 6: X-ray study of nematic mesophases from V-shaped mesogens. A: Diffraction pattern of 2c at 70 °C. B: Model of the local molecular order
and characteristic distances corresponding to reflections (i) and (ii).
work is in progress in order to draw a more detailed picture of the magnetic field, thus leading only to uniaxial nematic phases.
the supramolecular organisation of thiadiazole derivatives 1 and Work is in progress to synthesise molecules with a smaller
2 in their nematic phase.
bending angle in order to induce possibly a biaxial order at high
temperature.
Conclusion
Thiadiazole nematogens with ester groups connected via Experimental
alkyloxy spacers could be efficiently prepared by a previously Chemicals were obtained from Fisher Scientific and Sigma-
reported two-step procedure. These mesogens are capable of Aldrich and used as received. The synthesis of compounds 4
hydrogen bonding if the esters are cleaved. The mesophase [23,25] and 7 [24] was described previously. Column chromato-
range and the melting temperature reach an optimum when the graphy was carried out on silica 60 (Merck, mesh 70–230). PFT
nematogens are desymmetrised with a butoxy and a heptyloxy 1H and 13C NMR spectra were recorded in CDCl3 with a Varian
spacer. For this molecule, optical observations by conoscopy Oxford 400 MHz spectrometer with the residual solvent signal
monitored a uniaxial nematic phase over the whole temperature at 7.26 ppm as a reference. Mass spectra were obtained on a
range of 150 °C upon cooling from the isotropic phase to room Finnigan MAT95 (FD MS). Elemental analysis was carried out
temperature. X-ray diffraction points to the alignment of two in the microanalytical laboratory at the University of Mainz.
axes in the magnetic field in this family of mesogens. Both POM observations were made with a Zeiss Axioscop 40
features may be rationalised if larger assemblies of V-shaped equipped with a Linkam THMS600 hot stage. DSC was
molecules are isotropically distributed around the direction of performed using a Perkin Elmer Pyris 1.
Table 2: X-ray diffraction data. The correlation length ξ was estimated from the half width of the reflections by using the Scherrer formula [33,34].
Compound
T [°C]
105
80
d (i) [Å](ξ/d)
d (ii) [Å](ξ/d)
d (iii) [Å](ξ/d)
d (iv) [Å](ξ/d)
1a
2a
1c
2c
1e
15.1
(4.0)
10.2
(4.2)
4.3
(5.2)
4.6
(4.3)
14.9
(4.1)
9.8
(4.4)
4.2
(5.3)
4.4
(4.7)
100
70
15.7
(3.4)
9.3
(4.3)
4.4
(5.4)
4.6
(4.1)
15.2
(2.4)
9.5
(6.3)
4.0
(6.1)
4.7
(3.7)
105
16.4
(2.8)
9.5
(4.3)
4.4
(5.4)
4.6
(3.9)
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Beilstein Journal of Organic Chemistry 2009, 5, No. 73.
X-ray diffraction measurements were carried out on powder 2,5-Bis-{4-[4-{4-[4-(ethoxycarbonyl)butoxy]phenylethynyl}-
samples in glass capillaries of 1.5 mm diameter. The nematic 2,5-bis(hexyloxy)phenyl]ethynylphenyl}-1,3,4-thiadiazole
phases were aligned in a magnetic field (1T) upon cooling from (1a) Hexane/EtOAc = 6/1 (Rf = 0.1), yellow solid; yield 120 mg
the isotropic to the nematic phase. The WAXS measurements (74%). 1H NMR (400 MHz, CDCl3): δ = 8.00 (4H, AA′BB′),
were performed by using a standard copper anode (2.2 kW) 7.64 (4H, AA′BB′), 7.46 (4H, AA′BB′), 7.02 (s, 2H), 7.01 (s,
source with pinhole collimation equipped with a X-ray mirror 2H), 6.86 (4H, AA′BB′), 4.13 (q, 4H, COOCH2CH3, J = 7.2),
(Osmic typ CMF15-sCu6) and a Bruker detector (High-star) 4.04 (t, 4H, OCH2, J = 6.4), 4.03 (t, 4H, OCH2, J = 6.4), 3.98 (t,
with 1024 × 1024 pixels. The diffraction data were calibrated 4H, OCH2, J = 6.4), 2.34 (t, 4H, CH2COOEt, J = 7.2), 1.85 (m,
by using silver behenate as a calibration standard [37]. The 16H, CH2), 1.55 (m, 8H, CH2), 1.37 (m, 16H, CH2), 1.26 (t,
X-ray patterns were evaluated using the datasqueeze software 6H, CH3, J = 7.2), 0.91 (t, 6H, CH3, J = 7.2), 0.90 (t, 6H, CH3,
(http://www.datasqueezesoftware.com/).
J = 7.2); 13C NMR (100 MHz, CDCl3): δ = 173.6 (Cq, C=O),
167.8 (Cq, N=C–S), 159.2 (Cq, C–OCH2), 154.0, 153.5 (Cq,
C–OC6H13), 133.2, 132.3 (Ct), 129.6 (Cq), 127.9 (Ct), 126.7
(Cq), 117.0, 116.8 (Ct), 115.5, 115.2 (Cq), 114.6 (Ct), 112.9
General method for preparation of interme-
diate products 3a–e
The mixture of 1.0 equiv of thiadiazole 7, 1.0 equiv of the cor- (Cq), 95.5, 94.1, 89.2, 84.7 (C≡C), 69.8, 69.7, 67.6 (OCH2),
responding terminal alkyne 6a–e, 0.1 equiv of Pd(PPh3)4 and 60.5 (COOCH2CH3), 34.1 (CH2COOEt), 31.8, 29.4, 28.7, 25.9,
0.05 equiv of CuI in piperidine is stirred for 2 h at room tem- 22.81, 22.79, 21.7 (CH2), 14.4, 14.2 (CH3); EA: Calc. for
perature. Subsequently, the solvent is removed in vacuo and the C84H98N2O10S: C 75.99, H 7.44, N 2.11, S 2.41; Found: C
products are isolated by column chromatography using a mix- 75.94, H 7.47, N 2.05, S 2.42; FD MS: m/z [%]: 1325.9 (100,
ture of EtOAc/hexane.
M+); 663.1 (70, M2+).
2-{4-[4-{4-[4-(Ethoxycarbonyl)butoxy]phenylethynyl}-2,5-
bis(hexyloxy)phenyl]ethynylphenyl}-5-(4-bromophenyl)-
1,3,4-thiadiazole (3a) Hexane/EtOAc = 6/1 (Rf = 0.25), yellow
solid; yield 0.12 g (78%). 1H NMR (400 MHz, CDCl3): δ =
7.99 (2H, AA′BB′), 7.89 (2H, AA′BB′), 7.64 (4H, AA′BB′),
7.46 (2H, AA′BB′), 7.02 (s, 1H), 7.01 (s, 1H), 6.86 (2H,
AA′BB′), 4.14 (q, 2H, COOCH2CH3, J = 7.2), 4.05 (t, 2H,
OCH2, J = 6.4), 4.04 (t, 2H, OCH2, J = 6.4), 3.99 (m, 2H,
OCH2), 2.39 (t, 2H, CH2COOEt, J = 7.2), 1.85 (m, 8H, CH2);
1.55 (m, 4H, CH2); 1.36 (m, 8H, CH2); 1.26 (t, 3H, CH3, J =
7.2); 0.91 (t, 3H, CH3, J = 7.2), 0.90 (t, 3H, CH3, J = 7.2); 13C
NMR (100 MHz, CDCl3): δ = 173.8 (Cq, C=O), 167.9, 167.2
(Cq, N=C–S); 159.3 (Cq, C–OCH2), 154.0, 153.3 (Cq,
C–OC6H13), 133.2, 132.6, 132.4 (Ct), 129.4 (Ct), 129.1 (Cq),
127.9 (Ct), 126.8, 125.8 (Cq), 117.0, 116.8 (Ct); 115.4, 115.2
(Cq), 114.6 (Ct), 112.9 (Cq), 95.6, 94.0, 89.2, 84.7 (C≡C), 69.8,
69.7, 67.8 (OCH2), 60.4 (COOCH2CH3), 34.4 (CH2COOEt),
31.7, 29.5, 29.4, 29.0, 25.9, 25.8, 24.8, 22.8 (CH2), 14.4, 14.2
(CH3); EA: Calc. for C59H53BrN2O5S: C 68.28, H 6.20, N 3.25,
S 3.72; Found: C 68.38, H 6.31, N 3.33, S 3.70; FD MS: m/z
[%]:861.7 (87, [M+2]+); 859.7 (100, M+).
Supporting Information
Supporting Information File 1
Synthetic procedures and analytical results for compounds
1b–e, 2a–g, 3b–e, 5a–e and 6a–e.
[http://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-5-73-S1.doc]
Acknowledgments
We are grateful to the Bundesministerium für Bildung und
Forschung (BMBF) and the Deutsche Forschungsgemeinschaft
(DFG) for their financial support. We thank Prof. Herbert
Meier, Annette Oehlhof and Dr. Norbert Hanold for the possi-
bility to realize the FD MS and elemental analysis at the
University of Mainz. We are especially grateful to Michael
Bach and Prof. Jochen Gutmann for their support during X-ray
measurements at the Max Planck Institute for Polymer Research
in Mainz.
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