Thermotropic and lyotropic behaviour of new liquidcrystalline materials with different hydrophilic groups: Synthesis and mesomorphic properties

Article abstract of DOI:10.3762/bjoc.9.45

Several new calamitic liquid-crystalline (LC) materials with flexible hydrophilic chains, namely either hydroxy groups or ethylene glycol units, or both types together, have been synthesized in order to look for new functional LC materials exhibiting both

Full text of DOI:10.3762/bjoc.9.45

Thermotropic and lyotropic behaviour of new liquid-
crystalline materials with different hydrophilic
groups: synthesis and mesomorphic properties
Alexej Bubnov*1,§, Miroslav Kašpar1, Věra Hamplová1, Ute Dawin2
and Frank Giesselmann2
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2013, 9, 425–436.
1Institute of Physics, Academy of Sciences of the Czech Republic, Na
Slovance 2, 182 21 Prague, Czech Republic and 2Institute of Physical
Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569
Stuttgart, Germany
doi:10.3762/bjoc.9.45
Received: 12 September 2012
Accepted: 03 February 2013
Published: 25 February 2013
Email:
Alexej Bubnov* - bubnov@fzu.cz
Associate Editor: P. J. Skabara
* Corresponding author
© 2013 Bubnov et al; licensee Beilstein-Institut.
License and terms: see end of document.
§ Tel.: +420266052134; Fax: +420286890527
Keywords:
contact cell preparation; hydrophilic chain; lamellar phase; lyotropic
liquid crystal; thermotropic liquid crystal
Abstract
Several new calamitic liquid-crystalline (LC) materials with flexible hydrophilic chains, namely either hydroxy groups or ethylene
glycol units, or both types together, have been synthesized in order to look for new functional LC materials exhibiting both, ther-
motropic and lyotropic behaviour. Such materials are of high potential interest for challenging issues such as the self-organization
of carbon nanotubes or various nanoparticles. Thermotropic mesomorphic properties have been studied by using polarizing optical
microscopy, differential scanning calorimetry and X-ray scattering. Four of these nonchiral and chiral materials exhibit nematic and
chiral nematic phases, respectively. For some molecular structures, smectic phases have also been detected. A contact sample of
one of the prepared compounds with diethylene glycol clearly shows the lyotropic behaviour; namely a lamellar phase was
observed. The relationship between the molecular structure and mesomorphic properties of these new LCs with hydrophilic chains
is discussed.
Introduction
All materials showing liquid-crystalline (LC) behaviour belong partially rigid anisotropic molecules. Amphiphilic compounds
to two general classes: lyotropic materials, in which fluid can form a variety of thermotropic liquid-crystalline phases as a
anisotropy results from interactions between anisotropic aggre- function of temperature by themselves, and lyotropic liquid-
gates of amphiphilic molecules; and thermotropic materials, in crystalline phases upon addition of some solvent, such as water
which the orientational order arises from interactions among or diethylene glycol [1]. Thermotropic liquid-crystalline
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systems composed of amphiphilic molecules can exhibit challenging issues such as the organization of carbon nanotubes
smectic phases with layered structure [2] or nematic (eventu- [17] or various nanoparticles [18] in a liquid-crystalline matrix.
ally cholesteric) phases. Lyotropic systems usually form a To reach the goal, several new multifunctional liquid-crys-
lamellar liquid-crystalline mesophase, i.e., a lyotropic analogue talline materials possessing either ethylene glycol units
of the thermotropic orthogonal smectic A (SmA) phase [3], and (denoted as TL1 and TL2) or a different number of hydroxy
more rarely nematic, columnar and cubic mesophases [4,5].
groups (denoted as TL3 and TL4 [26-28]) or both types of
these hydrophilic groups together and an additional photosensi-
Combination of thermotropic and lyotropic properties for ma- tive azo group in the molecular core (denoted as TL5) have
terials with definite molecular structure has been intensively been designed, synthesized and studied (see Table 1 for the
studied so far [6-16] and is of high importance in particular for chemical structures). Compound TL4 with a decyloxy end
developing new types of functional LC materials [15,17,18]. group and a hexyl spacer was described in [28] along with a
Series of alkyl glucosides and related materials usually possess similar compound having a hexyloxy end group. A compound
thermotropic mesophases [16] as well as lyotropic columnar that carries a hexyloxy group and a pentyl spacer has been
phases in water solution [3]. The thermotropic SmA phase and studied recently [27]; mesomorphic behaviour of this material
hexatic/cubic/lamellar lyotropic phases have been detected for a was very similar to that of TL4. Corresponding mesophases N*
series of 4-alkoxyphenyl β-D-glucopyranosides [5]. LC com- and SmC* were also observed for the chiral compound in [26]
pounds in which a hydrophilic polyethyleneimine chain with having the same molecular core as TL4 but a branched chiral
hydroxy side-groups is attached to the azobenzene mesogenic alkoxy chain instead of the decyloxy group used for TL4. The
core through the alkylene chain have showed a thermotropic relation between the molecular structure and mesomorphic
SmA phase, lyotropic lamellar phase, and a lyotropic analogue properties of these new multifunctional compounds with
of the tilted smectic C phase [2]. Due to microsegregation of the different structures is discussed.
hydrophilic regions from aromatic segments in the absence of
Results and Discussion
flexible alkyl chains, the thermotropic and lyotropic smectic
and columnar phases have been detected for 4-benzyloxy-4’- Thermotropic behaviour
(2,3-dihydroxypropyloxy)biphenyls with lateral methyl Mesomorphic properties
substituents [19]. Several silver-containing thermotropic liquid- For the studied materials, sequences of phases were determined
crystalline materials based on bis(stilbazole) silver(I) cation in by characteristic textures and their changes were observed in a
association with the amphiphilic counter-ion lauryl sulfate ex- polarizing optical microscope (POM). The phase-transition
hibit lyotropic and thermotropic liquid-crystalline behaviour temperatures and transition enthalpies were evaluated from
[20]. A series of monoalkyl glycosides possesses a very stable differential scanning calorimetry (DSC) measurements. Ther-
thermotropic SmA phase as well as lyotropic lamellar, cubic motropic liquid-crystalline properties of all compounds under
and even hexagonal phases depending on the amount of the study are summarized in Table 2.
added water used as a solvent [4]. Intensive studies have been
done on long-alkyl-chain glycopyranosides with monosac- On cooling from the isotropic state, TL1 and TL4, with quite a
caride [21] and disaccharide [22] and compounds with different structure of the molecular core and aliphatic chains
pH-sensitive [23] head groups. For these types of compounds (see Table 1 for the difference in molecule structure), possess
the thermotropic SmA and cubic phases have been detected. In the nematic phase. The tilted smectic phase (SmC) being
addition, rich lyotropic polymorphism has also been found, partially monotropic in character (i.e., the high temperature part
namely cubic phases and lamellar phases as well as the of the phase is enantiotropic) has been observed on cooling
lyotropic cholesteric phase [21-23]. An effort to identify the below the nematic phase. For TL4, the temperature of the
role of the hydroxy group in the mesomorphic behaviour of Iso–N phase transition (157 °C) is found to be pronouncedly
alkyl glycosides has been made recently [24]. The methyl 6-O- higher than that observed for TL1. Below the SmC phase a
(n-acyl)-α-D-glucopyranosides, with chain lengths between crystal modification (denoted as Cr1 phase) has been detected
dodecanoyl and hexadecanoyl exhibit a monotropic SmA phase for TL4 and TL1. For TL3 no liquid-crystalline behaviour has
(i.e., occurring explicitly on cooling) only [25]. Even though a been detected: only a modification of a crystalline phase
lot has already been done, many open questions still remain.
(denoted as Cr1) exists within quite a broad temperature range.
The objective of this work is to contribute to a better under- In Figure 1 microphotographs of textures for TL1 taken under
standing of the chemical-structure–physical-property relation- different temperature and alignment conditions are presented,
ship for materials forming both, thermotropic and lyotropic namely the marbled texture of the nematic phase obtained at
mesophases. This understanding is of high potential interest for 110 °C on a planar cell (Figure 1a), the schlieren texture of the
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Beilstein J. Org. Chem. 2013, 9, 425–436.
Table 1: Chemical formulae of compounds and used abbreviations.
Notation
Chemical formula
TL1
4'-(2,5,8,11-tetraoxatridecan-13-yloxy)biphenyl-4-yl 4-(decyloxy)benzoate
TL2
TL3
4'-(2,5,8,11-tetraoxatridecan-13-yloxy)biphenyl-4-yl 4-(2-methylbutoxy)benzoate
2-(1-(6-(4'-(6-(3-hydroxy-2-(hydroxymethyl)-2-methylpropoxy)hexyloxy)biphenyl-4-yloxy)hexyloxy)methyl)-2-
methylpropane-1,3-diol
TL4
TL5
4'-(6-(3-hydroxy-2-(hydroxymethyl)-2-methylpropoxy)hexyloxy)biphenyl-4-yl 4-(decyloxy)benzoate
(E)-2-methyl-2-((2-(2-(2-(4-((4-((4-(2-methylbutoxy)phenyl)diazenyl)phenoxy)methyl)phenoxy)ethoxy)ethoxy)
ethoxy)methyl)propane-1,3-diol
Table 2: Sequence of phases and phase-transition temperatures, T (°C), measured on cooling (5 K min−1); melting points, mp (°C), measured on
heating (5 K min−1) and phase-transition enthalpies, ΔH [Jg−1], obtained by DSC for the studied compounds.a
mp
phase
Cr2
T/ΔH
phase
Cr1
–
T/ΔH
phase
SmC
–
T/ΔH
phase
N
T/ΔH
phase
T/ΔH
Iso
●
TL1
(nonchiral)
70
[+19.0]
54
[−18.1]
90
[−16.3]
102
[−3.5]
115
[−2.0]
–
BPII
–
TL2
(chiral)
80
[+39.9]
Cr2
70
[−36.0]
N*
–
103
[−0.7]
104
[msc]
●
TL3
(nonchiral)
74
[+39.9]
Cr2
69
[−43.0]
Cr1
Cr1
–
117
[−67.6]
–
●
TL4
(nonchiral)
76
[+82.9]
Cr2
58
[−45.1]
109
[−62.9]
SmC
SmC*
147
[−17.6]
N
157
[−9.6]
–
●
TL5
95
Cr2
86
113
N*
120
–
●
(chiral)
[+7.6]
[−5.6]
[−0.7]
[−16.5]
a(“●” - the phase exists; “–” - the phase does not exist; “[msc]” - determined by observations in POM only).
nematic phase obtained at 108 °C on free-standing films (FSF) DSC plot on heating/cooling runs for indicated nonchiral TL1,
(Figure 1b), and the N–SmC phase transition obtained at about TL3 and TL4 and for chiral TL2 and TL5 are presented in
102 °C on FSF (Figure 1c).
Figure 2 and Figure 3, respectively. The blue phase (BPII) and
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Beilstein J. Org. Chem. 2013, 9, 425–436.
Figure 1: Microphotographs of the textures obtained in the polarized optical microscope on planar samples (PS) and free-standing films (FSF) as indi-
cated: (a) The nematic phase at 110 °C for TL1 (PS); (b) the nematic phase at 108 °C for TL1 (FSF); (c) the N–SmC phase transition at about 102 °C
for TL1 (FSF); (d) the chiral nematic N* phase at 111 °C for TL5 (PS); (e) “broken fans” of the SmC* phase at 106 °C for TL5 (PS). (Width of the
photos is about 300 μm).
Figure 2: DSC plot on heating/cooling runs (indicated by horizontal arrows) for indicated nonchiral compounds: TL4 (a), TL1 (b) and TL3 (c). The
detected mesophases are indicated.
the cholesteric phase (N*) have been detected for the chiral the spontaneous quantities in detail, namely the spontaneous
TL2. The peak corresponding to the Iso-BPII phase transition polarization and tilt angle. For this compound the micropho-
has not been detected by DSC and the temperature of this phase tographs of textures obtained in POM are shown on Figure 1d
transition has been taken from observations obtained by POM and Figure 1e for the chiral nematic N* phase at 111 °C (planar
(Table 2). The type of the blue phase (BPII) has been deter- sample) and for the ferroelectric tilted SmC* phase (broken fans
mined by the characteristic platelet texture (similar to that texture) at 106 °C, respectively.
presented in [29]) observed on planar samples by POM. Chiral
X-ray scattering
TL5 with an azo group in the molecule core possesses the chiral
nematic phase and the tilted ferroelectric smectic C* phase.
Ferroelectric electro-optic switching has been clearly detected
in the SmC* phase but due to the monotropic (supercooled)
character of the phase it was not possible to measure and study
The structures of the mesophases formed in the studied com-
pounds have been checked by X-ray scattering. As an example,
the temperature dependence of the smectic layer spacing d, for
TL1 is shown in Figure 4. The MOPAC/AM1 model has been
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Beilstein J. Org. Chem. 2013, 9, 425–436.
Figure 3: DSC plot on heating/cooling runs (indicated by horizontal arrows) for indicated chiral compounds: TL2 (a) and TL5 (b). The detected
mesophases are indicated.
used to calculate the length of TL1 in the energy-optimized
conformation, which gives 41 Å for the most extended
conformer. In X-ray data taken at small scattering angles in the
nematic phase, a peak of quite a low intensity corresponding to
this scattering usually approximately matches the molecular
length and could also give evidence of the pretransitional
smectic order. For TL1, these values are substantially lower
than the calculated length of the most extended conformer. This
fact gives evidence for the bent-like conformation of the mole-
cule, i.e., the molecule core is rigid but the flexible chains are
bent and not extended at all. The increase of scattered X-ray
signal intensity on cooling also confirms the increase of the
order with temperature decrease (Figure 4). In the SmC phase,
the decrease of the d values is due to the increase of the mole-
cule tilt angle on cooling. The width of the mesophases and
hence the phase-transition temperatures detected from the X-ray
analysis are slightly shifted with respect to those determined
from the DSC (Table 2) due to a different cooling rate.
Lyotropic behaviour
In this section preliminary studies of lyotropic behaviour by
means of contact preparation are presented.
Figure 4: Temperature dependence of the layer spacing d, and inten-
sity of the scattered X-ray beam measured at small angles in the
Contact preparation
The cells for the contact preparation were prepared as schemati-
cally presented in Figure 5. On a glass slide an amount of the
material (several milligrams) was melted into the isotropic
phase (Figure 5a). The liquid was covered by another glass slide
in such a way that only half of the area between the slides was
filled by the LC material (Figure 5b). At the LC–air interface a
drop of water or diethylene glycol (DG) was placed close to the
cover glass on one side only, in order to ensure that water or
DG fills the air gap at the LC border without leaving air bubbles
(Figure 5c). The thickness of the cell is not fixed, but prefer-
nematic, SmC and crystalline phases for TL1. Values of the layer
spacing obtained in the nematic phase correspond to the length of the
molecule.
ably is within 10–50 μm, which can be detected by interferom-
etry. Contact samples were studied by using POM up to the
evaporation temperature of the solvent (which is not desirable
as the solvent condensates on the lenses of the POM objective).
The cells described above are easy to prepare and very conveni-
ent for primary identification of the lyotropic behaviour if any
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Figure 5: Schematic contact preparation used for detection and study of lyotropic behaviour.
exists. Sealed samples with well-defined thickness (fixed by the phase diagram are necessary (in progress now; will be
spherical glass spacers, Figure 5a) were also used. A special presented elsewhere) in order to get more quantitative results on
silicon glue stable up to 250 °C was used for sealing (Figure 5c) the lyotropic behaviour of TL4.
preventing evaporation of the solvent (usually water or DG).
Discussion of the molecular structure –
Mesomorphic lyotropic behaviour
mesomorphic property relationship
TL1–TL5 were tested for lyotropic behaviour by using the It is quite obvious that the structure of the molecular core as
contact-cell preparation technique. For our studies, water and/or well as the presence of additional terminal hydroxy groups or
diethylene glycol were used as the solvent. However, after alkyl chains should significantly influence the mesomorphic
careful testing of all the materials only TL4 clearly shows the properties of LC materials. Recently, two series of chiral liquid-
lyotropic phase in contact with diethylene glycol starting at the crystalline materials (similar to those presented in this work)
temperature of 109 °C, which is lower than the thermotropic with chiral lactate group or lactic acid derivative have been
crystal–LC phase-transition temperature (Tcryst–LC = 113 °C). synthesized and studied [30-32]. These materials (with the same
On heating, the solvent visibly penetrates into the liquid-crys- molecular core and nonchiral chain as TL4) possess different
talline area of TL4 material indicating the solubility. Figure 6a thermotropic LC phases depending on the chiral chain structure.
shows the overview of the contact area. Figure 6b,c provides a However, the temperatures of the phase transitions are remark-
microphotograph of a close-up of the lyotropic area. The ably lower for these chiral materials than are those for TL4, as
myelinic streaks can be taken as clear evidence for the exis- the introduction of two hydroxy groups instead of the chiral
tence of the lamellar phase. However, more detailed studies of chain usually results in an increase of the clearing point.
Figure 6: Microphotographs of the contact preparation of TL4 with diethylene glycol (DG): (a) texture of the lamellar phase (on top) at about 109.0 °C
(width of the photo is approx. 350 μm); (b) and (c) close-up texture of the lyotropic area: myelinic streaks appear within a few seconds and remain
stable; black area on top of the microphotographs corresponds to homeotropic orientation of the lamellar phase or isotropic liquid regions of mainly
DG (width of the photo is about 150 μm).
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Beilstein J. Org. Chem. 2013, 9, 425–436.
Mesomorphic properties of TL5 with two hydroxy groups can nonchiral TL3 and chiral TL2. TL3 possesses no liquid-
be compared to those of the chiral compounds with terminal crystalline phases but only crystalline ones. Lyotropic behav-
acrylic group in the nonchiral chain prepared as monomers for iour has been tested for all LC materials by using a contact
side-chain polyacrylates [33,34]. All these compounds clearly preparation technique, which has been described in detail. A
possess the LC behaviour and exhibit the chiral nematic phase contact sample of TL4 with diethylene glycol clearly shows the
and also the chiral smectic phases. No pronounced difference in lyotropic behaviour, namely a lamellar phase was detected.
clearing point has been found in cases where the molecule core While looking for advanced functional LC materials, such a
is the same as for TL5 but the nonchiral chain with a double type of molecular structure seems to be promising for further
bond is replaced by that with two hydroxy groups. However, a studies, which are in progress now and will be presented else-
minor increase in the melting point (about 10 K) has been where.
observed for TL5 with respect to that of the chiral acrylates
Experimental
[34].
Synthesis
Quite remarkable observations can be made while comparing The synthetic procedure for the liquid-crystalline diol with a
the mesomorphic properties of TL2 with those of a compound 1,3-propandiol group connected by a flexible spacer to the
possessing the same molecular core and chiral centre but mesogenic part of the molecule and with two hydroxy groups
differing in the nonchiral chain, i.e., an ethylene glycol unit has (4'-(6-(3-hydroxy-2-(hydroxymethyl)-2-methylpropoxy)hexyl-
been used instead of the alkyl chain [35]. The presence of oxy)biphenyl-4-yl 4-(decyloxy)benzoate), denoted as TL4, has
ethylene glycol units destroys the smectic order. Hence, the been presented in [28]. The synthesis of the other compounds is
chiral nematic phase is favoured by TL2 instead of the tilted presented in this section. Structures of the intermediate and final
ferroelectric SmC* phase observed for the compound with the products were confirmed by 1H nuclear magnetic resonance
nonchiral alkyl chain. However, the presence of the ethylene spectroscopy by using a 300 MHz Varian spectrometer in solu-
glycol units suppresses the clearing point by more than 30 K for tions with CDCl3 or dimethylsulfoxide (DMSO) with tetra-
TL2 compared to that for a material with a typical alkyl chain methylsilane as an internal standard. The chemical purity of the
[35].
compounds was checked by high performance liquid chroma-
tography, which was carried out with an Ecom HPLC chro-
While searching for new LCs exhibiting both the thermotropic matograph by using a silica-gel column (Separon 7 μm,
and lyotropic behaviour, materials with a hydrophilic ethylene 3 × 150, Tessek) with a 98/2 mixture of toluene and methanol
glycol chain (TL1 and TL2) instead of the frequently used as eluent (typical flow rate 1 mL/min, retention times for com-
hydrophobic alkyl terminal chains have been synthesized. pounds TL1–TL5 being from 3 min to 12 min). Detection of
However, our studies by contact preparation show that no the eluting products was done by UV–vis detector (λ = 290 nm).
lyotropic behaviour is present. Moreover, the symmetric, For TL2 and TL5 the chiral centres are in (S)-configuration.
strongly hydrophilic material with diol moieties at the end of The chemical purity of all synthesised compounds was found
both alkyl chains (TL3) also does not possess the lyotropic within 99.5–99.9%.
behaviour, and even the thermotropic one is absent. A combina-
tion of the ethylene glycole group together with a terminal diol Preparation of TL1 and TL2
moiety on both alkyl chains (TL5) has been also found useless The general procedure for the synthesis of compounds
for the presence of simultaneous thermotropic and lyotropic possessing ethylene glycol units is presented in Scheme 1.
behaviour. Only asymmetric TL4 with a diol moiety termi- Phenol 2 was prepared as follows. A mixture of 41 g (0.2 mol)
nating one alkyl chain possesses both, thermotropic and tetraethylene glykol monomethyl ether 1 (TEG) and 64 g of dry
lyotropic phases.
pyridine was reacted with 41 g of tosyl chloride at −5 °C for
2 hours. Then the mixture was stirred at room temperature for
3 hours and poured into 250 g of ice with 100 mL of concen-
Conclusion
Several new liquid-crystalline materials possessing either two trated hydrochloric acid. The product was then extracted three
or four hydroxy groups or ethylene glycol units, or both types times by benzene; the organic layer was washed with cold HCl,
together, have been synthesized and studied with the aim to dried with potassium carbonate, filtered and evaporated. The
look for new functional liquid-crystalline materials exhibiting yield was 40 g of a yellow viscous liquid of TEG-tosylate.
the thermotropic and lyotropic behaviour. Most of these new 1H NMR (CDCl3, 300 MHz) for the intermediate product TEG-
nonchiral and chiral materials exhibit the thermotropic nematic tosylate δ (ppm) 7.72 (d, 2H, ortho to SO3), 7.30 (d, 2H, ortho
and chiral nematic phases, respectively. Smectic phases have to CH3), 4.10 (t, 2H, CH2OAr), 3.65–3.45 (m, 14H, CH2O),
been detected for the studied materials with the exception of 3.30 (s, 3H, CH3O), 2.38 (s, 3H, CH3Ar).
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Beilstein J. Org. Chem. 2013, 9, 425–436.
Scheme 1: General procedure for the synthesis of (a) nonchiral 4'-(2,5,8,11-tetraoxatridecan-13-yloxy)biphenyl-4-yl 4-(decyloxy)benzoate (TL1) and
(b) chiral 4'-(2,5,8,11-tetraoxatridecan-13-yloxy)biphenyl-4-yl 4-(2-methylbutoxy)benzoate (TL2) with ethylene glycol units.
A mixture of 68 g (0.188 mol) of TEG–tosylate and 38 g a potassium hydroxide/ethanol mixture. Afterwards the solu-
(0.2 mol) of 4,4‘-biphenol was dissolved in 0.5 L ethanol/water tion was acidified by HCl, extracted by diethyl ether/acetone,
(1:1) and heated under reflux. Sodium hydroxide (12 g) dried by potassium sulfate and evaporated in vacuum. The yield
dissolved in 50 mL of water was added drop by drop over was 23 g (0.06 mol, 30.5%). 1H NMR of the intermediate prod-
several hours. Boiling under reflux was continued for 4 days, uct 2 (DMSO, 300 MHz) δ (ppm) 7.50 and 7.41 (dd, 4H, ortho
the solution was then acidified with hydrochloric acid, ethanol to –Ar), 6.98 (d, 2H, ortho to –OR), 6.81 (d, 2H, ortho to –OH),
was evaporated, and the aqueous mixture was left to stand in the 4.11 (t, 2H, CH2OAr), 3.75 (t, 2H, CH2CH2OAr), 3.60–3.40
refrigerator overnight. The crude substance was separated on (m, 12H, CH2O), 3.22 (s, 3H, CH3).
fritted glass and crystallized from ethanol. Purification of crude
phenol 2 was performed after its acetylation: 3 hours boiling Finally, TL1 and TL2 were obtained by conventional esterifica-
with acetanhydride followed by cooling the reaction mixture on tion with dicyclohexylcarbodiimide as condensation agent and
ice and further extraction of the product into dichloromethane. dimethylaminopyridine as catalyst in tetrahydrofurane solution.
This protected compound was purified by column chromatog- 1H NMR of TL1 (CDCl3, 300 MHz) δ (ppm) 8.18 (d, 2H, ortho
raphy on silica gel using mobile phase dichloromethane/acetone to –COO), 7.60–7.40 (m, 4H, ortho to –Ar), 7.23 (d, 2H, ortho
(97:3), and the acetyl group was then removed by hydrolysis in to –OCO), 6.98 (m, 4H, ortho to –OR), 4.18 (d, 2H,
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ArOCH2CH2O–), 4.05 (d, 2H, CH2OAr), 3.83 (d, 2H, (ppm) 7.50 (d, 4H, ortho to –Ar), 6.98 (d, 4H, ortho to –OR),
ArOCH2CH2O), 3.80–3.50 (m, 12H, CH2O), 3.40 (s, 3H, 4.00 (t, 4H, CH2OAr), 1.80 (quint., 4H, CH2CH2OAr),
OCH3), 1.90–1.20 (m, 20H, CH2), 0.90 (t, 3H, CH3).
1.60–1.20 (m, 12H, CH2), 0.80 (s, 6H,CH3).
1H NMR of TL2 (CDCl3, 300 MHz) 8.18 (d, 2H, ortho to Preparation of TL5
–OCO), 7.60–7.40 (m, 4H, ortho to –Ar), 7.23 (d, 2H, ortho to The general procedure for the synthesis of chiral TL5
–OCO), 6.98 (m, 4H, ortho to –OR), 4.18 (d, 2H, possessing two hydroxy groups and ethylene glycol units is
ArOCH2CH2O–), 4.08 (m, 2H,CH2OAr), 3.83 (d, 2H, presented in Scheme 3. The bromide 6 was prepared from 5 by
ArOCH2CH2O–), 3.80–3.50 (m, 12H, CH2O), 3.40 (s, 3H, similar methods as those presented in [36]. 1H NMR of the
OCH3), 1.90–1.30 (m, 3H, CH2CH), 0.90 (t + d, 6H, CH3). The intermediate product 6 (CDCl3, 300 MHz) δ (ppm) 7.30 (d, 2H,
optical rotation of TL2 was determined in chloroform by using ortho to CH2Br), 6.88 (d, 2H, ortho to –O), 4.50 (s, 2H,
a polarimeter from Optical Activity Ltd. as [α]D20 +3.1 (c 0.15, ArCH2Br), 4.12 (t, 2H, CH2OAr), 3.90–3.60 (m, 8H, CH2O),
CHCl3).
3.45 (t, 2H, CH2Br).
Preparation of TL3
The mesogenic phenol 7 was prepared according to the syn-
The synthetic procedure for the preparation of TL3 with four thetic procedure described in [36]. Intermediates 6 and 7 were
hydroxy groups is presented in Scheme 2. Diol 4 was prepared reacted in equal molar ratio by boiling in acetonitrile in the
from acetal 3 according to the procedure described previously presence of an excess of dry potassium carbonate for twenty
[28]. 1H NMR (CDCl3, 300 MHz) for intermediate diol 4 δ hours. The reaction mixture was poured into water; the precipi-
(ppm) 3.70–3.50 (dd, 4H, CH2OH), 3.40 (m, 6H, CH2Br, tate was filtered off and crystallized from acetone and from
CH2OCH2), 1.80 (quint., 2H, CH2CH2Br), 1.55 (quint., 2H, toluene. 1H NMR of intermediate product 8 (CDCl3, 300 MHz)
CH2CH2O), 1.40 (m, 4H, CH2), 0.80 (s, 3H, CH3).
δ (ppm) 7.86 (d, 4H, ortho to –N=N–), 7.39 (d, 2H, ortho to
CH2), 7.10–6.90 (ddd, 6H, ortho to –O), 4.15 (t, 2H,
The final compound 4,4´-biphenyl-bis(6-oxyhexyl-2,2-dimethy- ArOCH2CH2O), 3.90–3.60 (m, 10H, CH2O), 3.45 (t, 2H,
lolpropyl ether) was prepared by the boiling of 10 g of 4,4´- CH2Br), 1.90, 1.60, 1.30 (m, 3H, CH2C*H), 1.02 (d, 3H, CH3),
biphenol with an excess of diol 4 in anhydrous potassium 0.97 (t, 3H, CH3).
carbonate in acetone for 48 hours. The product was crystallized
from acetone and purified by column chromatography on silica Sodium hydride (0.1 mol) was slowly added to a solution of
gel; the yield was 38%. 1H NMR (CDCl3, 300 MHz) for TL3 δ 0.2 mol of 1,1,1- tris(hydroxymethyl)ethane (pentaglycerine) in
Scheme 2: General procedure for synthesis of 2-(1-(6-(4'-(6-(3-hydroxy-2-(hydroxymethyl)-2-methylpropoxy)hexyloxy)biphenyl-4-
yloxy)hexyloxy)methyl)-2-methylpropane-1,3-diol (TL3).
433

Beilstein J. Org. Chem. 2013, 9, 425–436.
Scheme 3: General procedure for the synthesis of chiral (E)-2-methyl-2-((2-(2-(2-(4-((4-((4-(2-
methylbutoxy)phenyl)diazenyl)phenoxy)methyl)phenoxy)ethoxy)ethoxy)ethoxy)methyl)propane-1,3-diol (TL5).
0.25 L dry dimethylformamide. After one hour of stirring at Thermotropic behaviour
room temperature (evolution of hydrogen), 0.05 mol of bro- Observation of the characteristic textures and their changes in
mide 8 was added and the reaction mixture was kept at POM was carried out on 12 μm thick glass cells, which were
50–60 °C overnight. Then the solvent was evaporated in filled with LC material in the isotropic phase by means of capil-
vacuum and the solid residue was extracted several times with lary action. The inner surfaces of the glass plates are covered by
water to remove excess pentaglycerine. The resulting yellow indium-tin-oxide electrodes and polyimide layers unidirection-
residue was dried in vacuum and the crude product purified by ally rubbed, which ensures planar alignment of the molecules,
column chromatography on silica gel using a mixture of chloro- e.g., bookshelf geometry in the smectic phase. In addition, for
form and ethanol (90:10) as eluent. The yield was 7 g (0.011 texture observation on samples with homeotropic alignment,
mol, 22%).
free-standing films have also been used. For the preparation of a
FSF, the liquid-crystalline material was mechanically spread
1H NMR of TL5 (CDCl3, 300 MHz) δ (ppm) 7.85 (d, 4H, ortho over a circular hole (diameter 3 mm) in a metal plate. A
to –N=N–), 7.38 (d, 2H, ortho to –CH2), 7.10–6.90 (ddd, 6H, LINKAM LTS E350 heating/cooling stage with a TMS 93
ortho to –O), 5.05 (s, 2H, Ar–CH2O), 4.15 (t, 2H, temperature programmer was used for temperature control,
ArOCH2CH2O), 3.90–3.60 (m, 16H, CH2OCH2, CH2OH), 3.53 which enabled temperature stabilisation within ±0.1 K.
(s, 2H, C–CH2O), 1.90, 1.60, 1.30 (m, 3H, CH2C*H), 1.03 (d, Phase-transition temperatures and enthalpies were determined
3H, CH3), 0.97 (t, 3H, CH3), 0.80 (s, 3H, C–CH3). The optical by differential scanning calorimetry (DSC - Pyris Diamond
rotation of TL5 was determined in chloroform, by using a Perkin-Elmer 7) on samples of 3–6 mg hermetically sealed in
polarimeter from Optical Activity Ltd., as [α]D20 +2.3 (c 0.05, aluminium pans in cooling/heating runs in a nitrogen atmos-
CHCl3).
phere at a heating/cooling rate of 5 K min−1. The temperature
434

Beilstein J. Org. Chem. 2013, 9, 425–436.
13.Xiao, D.; Wada, T.; Inoue, Y. Chirality 2009, 21, 110–113.
was calibrated from extrapolated onsets of the melting
points of water, indium and zinc. The enthalpy change was cali-
brated based on the enthalpies of melting of water, indium and
zinc.
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15.Shukla, R. K.; Raina, K. K.; Hamplová, V.; Kašpar, M.; Bubnov, A.
Phase Transitions 2011, 84, 850–857.
The small-angle X-ray scattering studies have been performed
with Ni-filtered Cu Kα radiation (wavelength λ = 1.5418 Å).
Small-angle scattering data from nonaligned samples (filled into
Mark capillary tubes of 0.7 mm diameter) were obtained by
using a Kratky compact camera (Aton Paar) equipped with a
temperature controller and a one-dimensional electronic
detector (M. Braun), the temperature being controlled within
0.1 K. For compounds possessing smectic phases, the layer
thickness, d, was determined from Bragg’s law nλ = 2dsinθ,
where d is calculated from the position of the small-angle (Θ =
0.2°–4.5°) diffraction peaks.
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Acknowledgements
The authors are very grateful to Dr. Milada Glogarová for
fruitful discussion of the results. This work was supported by
the Czech–German bilateral program ASCR–DAAD (Academy
of Science of the Czech Republic – German Academic
Exchange Service) No. D4-CZ5/10-11 and also by projects:
CSF P204/11/0723, ASCR M100101204, ASCR M100101211
and RMES 8815.
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