New pyridine based liquid crystalline esters with different terminal chains

Article abstract of DOI:10.1016/j.molstruc.2019.126930

The synthesis, structural and mesomorphic characterization of new pyridine-based methyl esters carrying a n-alkoxy chain or 3,7-Dimethyloctyloxy branched group at terminal have been presented. The liquid crystalline properties of the new pyridine-based calamitic molecules have been investigated by polarized optical microscopy and differential scanning calorimetry. New compounds exhibit enantiotropic smectic A mesophase at a variable mesomorphic range depending on alkoxy chain length and branching at terminal. The presence of a branched terminal group in chiral or racemic form gives rise to a sharply increase in mesomorphic range as well as decrease in crystallization points by preserving mesophase type.

Full text of DOI:10.1016/j.molstruc.2019.126930

Journal of Molecular Structure 1198 (2019) 126930
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
New pyridine based liquid crystalline esters with different terminal
chains
Gürkan Karanlık, Hale Ocak*, Belkız Bilgin Eran
Yildiz Technical University, Department of Chemistry, 34220 Esenler, Istanbul, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis, structural and mesomorphic characterization of new pyridine-based methyl esters car-
rying a n-alkoxy chain or 3,7-Dimethyloctyloxy branched group at terminal have been presented. The
liquid crystalline properties of the new pyridine-based calamitic molecules have been investigated by
polarized optical microscopy and differential scanning calorimetry. New compounds exhibit enantio-
tropic smectic A mesophase at a variable mesomorphic range depending on alkoxy chain length and
branching at terminal. The presence of a branched terminal group in chiral or racemic form gives rise to a
sharply increase in mesomorphic range as well as decrease in crystallization points by preserving
mesophase type.
Received 2 July 2019
Received in revised form
14 August 2019
Accepted 14 August 2019
Available online 15 August 2019
Keywords:
Liquid crystal
Calamitic molecule
Pyridine-based methyl esters
Smectic mesophase
© 2019 Elsevier B.V. All rights reserved.
1. Introduction
the molecule compared to the corresponding carbon homologues
and thereby affect the LC self-assembly, the phase transition tem-
Liquid crystals, which are one of the most fascinating classes of
advanced organic materials, have gained attention because of their
unique properties, which enables modern technological applica-
tions in numerous field such as organic light-emitting diodes,
electro-optics, biosensors, field-effect transistors, displays, photo-
voltaics and telecommunications [1e4].
Liquid crystals (LCs), which differ by the combination the
fluidity and long-range molecular order, exhibit various LC phases
depending on their polarisability, molecular rigidity, flexibility and
anisometric shape [5]. It is necessary to the investigation of the
structure - property relation in detail as well as molecular origin of
mesophases for the development of advanced applications of LC in
various fields.
Calamitic molecular shape provides a wide range of ways to
modify liquid crystalline properties by the change of linking units
between aromatic rings, introducing different terminal chains and
the presence of lateral substituents. The incorporation of hetero-
cyclic rings as a core into a liquid crystal molecule generates
advanced functional materials with an interesting mesogenic
behavior [6,7]. Heteroatoms such as nitrogen, oxygen and sulfur
lead to a change on the polarisability and the geometric shape of
peratures and dielectric behavior of the mesogens [8e14]. A various
mesogenic materials consisting of heterocyclic units such as pyri-
dine [15], thiophene [6,16] and 1,3,4-thiadiazole [10] as the core in
liquid-crystalline materials have been prepared.
Pyridine is one of the simplest heterocyclic aromatics used as a
core system inthe liquid crystalline molecules [17e23]. The posi-
tion of the nitrogen atom in the pyridine fragment and its position
in the molecular core considerably influence the liquid crystalline
properties of pyridine derivatives [24]. Although most rigid het-
erocyclic rings are not widely positioned at one of terminals of LC
molecule, pyridyl ring can be used as terminal groups of calamitic
liquid crystals to yield hydrogen-bonded LCs [25]. In addition, the
presence of two nitrogen atoms in rigid ring, e.g. phenyl-
pyrimidines, increase the polarity of the rigid core structure and
give rise to a smectic mesophase whereas the corresponding
biphenyl derivative with the same terminal alkyl chains is non-
mesomorphic [26].
Terminal substituents play an important role in mesogenic
systems. Chiral smectic liquid crystals which show mesomorphism
close to the room temperature have a great interest for the gener-
ation of displays based on ferroelectric materials with extremely
fast switching time [27]. The incorporation of asymmetric carbon
atom(s) to terminals leads to chiral LC phases that are formed by a
pure calamitic molecule [28].
* Corresponding author.
E-mail address: hocak@yildiz.edu.tr (H. Ocak).
In this paper, we report the synthesis, the structural and
https://doi.org/10.1016/j.molstruc.2019.126930
0022-2860/© 2019 Elsevier B.V. All rights reserved.

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G. Karanlık et al. / Journal of Molecular Structure 1198 (2019) 126930
mesomorphic characterization of new pyridine-based methyl es-
ters carrying a n-alkoxy chain or 3,7-Dimethyloctyloxy branched
terminal group in chiral or racemic form to meet the desired
properties of LC materials for device applications.
2.2.1. The Suzuki-Miyaura Cross-Coupling reaction procedure
[36,37] for the synthesis of new pyridine-based esters (3a-e) with
different terminal chains
In a 100 mL two-necked round-bottomed flask, commercially
available Methyl 5-bromopyridine-2-carboxylate (0.75 mmol) and
4-alkoxyboronic acids 2a-e (0.75 mmol) were dissolved in 1,2-
dimetoxyethane (15 mL) and then catalytic amount of Pd(PPh3)4
(0.0325 mmol) under Argon atmosphere. To this solution, saturated
aqueous solution of NaHCO3 was added and the reaction mixture
was heated to reflux for 3 h at 85 ꢀC. The end of the reaction was
monitored by TLC (hexane: ethyl acetate/3:1). After removing the
volatile components in vacuo, the resulting mixture was extracted
into CHCl3 (x 3) and the combined organic phases were washed
with saturated aqueous NaCl solution and dried over Na2SO4. The
solvent was removed under reduced pressure. The residue was
dissolved in chloroform and filtered on silica gel in order to remove
the catalyst. After evaporation of the solvent, the crude product was
purified by column chromatography on silicagel eluting with hex-
ane: ethyl acetate/3:1.
2. Experimental
2.1. Materials and instrumentation
New pyridine based liquid crystalline esters (3a-e) were char-
acterized 1H NMR, 13C NMR (Bruker Avance III 500 spectrometer, in
CDCl3 solution, with tetramethylsilane as internal standard) and
MS-QTOF (Agilent 6530, electrospray ionization, ion source: dual
ESI, MS abs. threshold: 200, MS/MS abs. threshold: 5, gas flow rate:
12 l/min, gas temperature 300 ꢀC). The optical rotation of com-
pounds (3d and 3e) were determined using Anton Paar, Model MCP
100 Modular circular polarimeter.
The liquid crystalline properties of compounds were investi-
gated by using a Mettler FP-82 HT hot stage and control unit in
conjunction with a Leica DM2700P polarizing microscope. DSC-
thermograms of chiral imine compounds were recorded on a
Perkin-Elmer DSC-6, heating and cooling rate: 10 ꢀC minꢁ1 in a
The optical rotation of compounds 3d and 3e was measured for
the proof of the optical purity.
The characterization of the final compounds is based on 1H, 13
C
NMR (Bruker Avance III 500 spectrometer, in CDCl3 solution, with
tetramethylsilane as internal standard). The detection of molecular
ions was performed by full MS electrospray ionization [MS ESI (þ)].
The proposed structures are in full agreement with the spectro-
scopic data.
nitrogen atmosphere.
20
589
(S)-(-)-
b
-citronellol (Aldrich, ꢂ99.0% ½
a
ꢃ
¼ ꢁ5.3ꢀ, neat), 3,7-
Dimethyloctanol (Sigma-Aldrich), 4-Bromophenol (Alfa Aesar),
Methyl 5-bromopyridine-2-carboxylate (Signma-Aldrich), K2CO3
(Merck), 1-Bromooctane (Merck), 1-Bromodecane (Merck), 1-Bro-
mododecane (Merck), Trimethylborate (Alfa Aesar), Tetrakis(-
2.2.2. Methyl 5-(4-n-octyloxyphenyl)pyridine-2-carboxylate (3a)
Yield: 49%, 0.125 g; colorless crystals. 1H-NMR (500 MHz,
triphenylphosphine)palladium(0)
(99%
Sigma-Aldrich),
n-
Butyllithium solution 2.5 M in hexanes (Sigma-Aldrich) and sodium
bicarbonate (technical) were purchased commercially. Solvents
were purchased or distilled. 1,2-Dimetoxyethane (Merck), 2-
CDCl3):
d
(ppm) ¼ 8.95 (dd, J z 2.4 Hz and 0.6 Hz, Pyridine Ar-H),
8.19 (dd, J z 8.2 Hz and 0.6 Hz, Pyridine Ar-H), 7.99 (dd, J z 8.2 Hz
and 2.4 Hz, Pyridine Ar-H), 7.58 (d, J z 8.8 Hz, 2 Ar-H), 7.03 (d,
J z 8.8 Hz, 2 Ar-H), 4.04e4.01 (m, 5H, OCH2 and OCH3), 1.85e1.80
(m, 2H, CH2), 1.52e1.46 (m, 2H, CH2), 1.41e1.26 (m, 8H, 4 CH2), 0.90
(t, J z 7.0 Hz, 3H, CH3). 13C-NMR (125 MHz, CDCl3):
€
Butanone (Merck) and THF (Riedel-de Haen, 99.9%) were pur-
chased commercially as dry solvents and were used without further
purification. Solvents used in the extraction and column chroma-
tography (hexane, ethyl acetate and chloroform) were distilled.
Thin-layer chromatography (TLC) was applied on aluminium plates
coated with silica gel 60 F254 (Merck) for intermediates. Column
chromatography was performed using silica gel 60 (Merck, pore
size 60 Å).
d
(ppm) ¼ 165.74 (CO), 160.07, 145.68, 139.48, 128.64 (Ar-C), 147.81,
134.33, 128.47, 125.22, 115.31 (Ar-CH), 68.22 (OCH2), 52.87 (OCH3),
31.80, 29.34, 29.23, 29.19, 26.02, 22.65 (CH2), 14.09 (CH3).
C
21H27NO3 MW: 341.44 g/mol. Full MS ESI (electrospray ionization)
(þ) [50.00e1000.00]: 341 (58) [Mþ], 282 (59) [Mþ-C2H3O2], 170
(100) [C11H8NO].
2.2. Synthesis and characterization of pyridine based liquid
crystalline esters
2.2.3. Methyl 5-(4-n-decyloxyphenyl)pyridine-2-carboxylate (3b)
Yield: 37%; 0.102 g; colorless crystals. 1H-NMR (500 MHz,
CDCl3):
d
(ppm) ¼ 8.95 (dd, J z 2.4 Hz and 0.8 Hz, Pyridine Ar-H),
The synthesis of pyridine-based calamitic esters 3a-e is given in
Scheme 1. Firstly, 4-Bromophenol was alkylated with the corre-
sponding n-alkyl bromide to give 4-alkoxybromobenzene 1a-e
[29e32]. 3,7-Dimethyloctyl bromide in racemic and chiral form
were prepared from commercially available 3,7-Dimethyl-1-
8.18 (dd, J z 8.1 Hz and 0.8 Hz, Pyridine Ar-H), 7.98 (dd, J z 8.1 Hz
and 2.4 Hz, Pyridine Ar-H), 7.57 (d, J z 8.8 Hz, 2 Ar-H), 7.03 (d,
J z 8.8 Hz, 2 Ar-H), 4.04e4.02 (m, 5H, OCH2 and OCH3), 1.86e1.80
(m, 2H, CH2),1.52e1.46 (m, 2H, CH2),1.41e1.30 (m, 12H, 6 CH2), 0.90
(t, J z 7.0 Hz, 3H, CH3). 13C-NMR (125 MHz, CDCl3):
octanol and (S)-(-)-
b
-citronellol. As described previously [33], (S)-
d
(ppm) ¼ 165.70 (CO), 160.11, 145.79, 139.46, 128.71 (Ar-C), 147.80,
(-)- -citronellol was firstly reduced by catalytic hydrogenation (H2,
b
134.25, 128.43, 125.15, 115.36 (Ar-CH), 68.26 (OCH2), 52.73 (OCH3),
31.85, 29.52, 29.50, 29.33, 29.25, 29.18, 25.99, 22.62 (CH2), 14.00
(CH3). C23H31NO3 MW: 369.50 g/mol. Full MS ESI (electrospray
ionization) (þ) [50.00e1000.00]: 370 (100) [Mþ], 310 (91) [Mþ-
C2H3O2], 172 (73) [C11H10NO].
Pd/C in MeOH) to obtain (S)-3,7-dimethyl-1-octanol. Then, both
alcohols reacted with. conc. aqu. HBr/conc. H2SO4 using tetrabu-
tylammonium hydrogensulfate (TBAHS) as catalyst to obtain the
corresponding 3,7-Dimethyloctyl bromides. Compounds 1a-e were
subjected to halogen-lithium exchange reaction by using n-butyl-
lithium in 2.5 M hexane solution, followed by the treatment with
B(OCH3)3 and then acidic hydrolysis to obtain 4-
alkoxybenzeneboronic acids 2a-e [29,31,34,35]. In the final step,
compounds 2a-e reacted with commercially available Methyl 5-
bromopyridine-2-carboxylate in 1,2-dimetoxyethane by using
Pd(PPh3)4 as catalyst and saturated NaHCO3 solution to yield the
target compounds 3a-e.
2.2.4. Methyl 5-(4-n-dodecyloxyphenyl)pyridine-2-carboxylate
(3c)
Yield: 50%; 0.149 g; colorless crystals. 1H-NMR (500 MHz,
CDCl3):
d
(ppm) ¼ 8.95 (dd, J z 2.3 Hz and 0.6 Hz, Pyridine Ar-H),
8.18 (dd, J z 8.2 Hz and 0.6 Hz, Pyridine Ar-H), 7.98 (dd, J z 8.2 Hz
and 2.3 Hz, Pyridine Ar-H), 7.57 (d, J z 8.8 Hz, 2 Ar-H), 7.03 (d,
J z 8.8 Hz, 2 Ar-H), 4.04e4.02 (m, 5H, OCH2 ve OCH3), 1.86e1.80 (m,

G. Karanlık et al. / Journal of Molecular Structure 1198 (2019) 126930
3
Scheme 1. Synthesis of new pyridine-based methyl esters (3a-e) with different terminal chains.
2H, CH2), 1.52e1.46 (m, 2H, CH2), 1.40e1.29 (m, 16H, 8 CH2), 0.90 (t,
J z 7.0 Hz, 3H, CH3). 13C-NMR (125 MHz, CDCl3):
2.2.5. Methyl 5-(4-(S)-3,7-dimethyloctyloxyphenyl)pyridine-2-
carboxylate (3d) [38]
Yield: 85%; 0.235 g; colorless crystals. 1H-NMR (500 MHz,
CDCl3):
8.19 (dd, J z 8.2 Hz and 0.6 Hz, Pyridine Ar-H), 7.99 (dd, J z 8.2 Hz
and 2.3 Hz, Pyridine Ar-H), 7.58 (d, J z 8.8 Hz, 2 Ar-H), 7.04 (d,
J z 8.8 Hz, 2 Ar-H), 4.11e4.03 (m, 5H, OCH2 ve OCH3), 1.91e1.84 (m,
1H, CH), 1.74e1.68 (m, 1H, CH), 1.66e1.51, 1.39e1.15 (2m, 8H, 4 CH2),
d
(ppm) ¼ 165.69
(CO), 160.11, 145.78, 139.46, 128.71 (Ar-C), 147.79, 134.26, 128.43,
125.15, 115.35 (Ar-CH), 68.26 (OCH2), 52.74 (OCH3), 31.87, 29.60,
29.58, 29.54, 29.53, 29.33, 29.29, 29.18, 25.99, 22.63 (CH2), 14.01
(CH3). C25H35NO3 MW: 397.55 g/mol. Full MS ESI (electrospray
ionization) (þ) [50.00e1000.00]: 398 (72) [Mþ], 338 (100) [Mþ-
C2H3O2], 172 (60) [Mþ-C11H10NO].
d
(ppm) ¼ 8.95 (dd, J z 2.3 Hz and 0.6 Hz, Pyridine Ar-H),

4
G. Karanlık et al. / Journal of Molecular Structure 1198 (2019) 126930
0.97 (d, J z 6.6 Hz, 3H, CH3), 0.89 (d, J z 6.6 Hz, 6H, 2CH3). 13C-NMR
(125 MHz, CDCl3):
Full MS ESI (electrospray ionization) (þ) [50.00e1000.00]: 370 (92)
d
(ppm) ¼ 165.63 (CO), 160.08, 145.49, 139.57,
[Mþ], 310 (75) [Mþ-C2H3O2], 170 (100) [Mþ-C11H8NO]. Optical
20
589
128.56 (Ar-C), 147.70, 134.48, 128.50, 125.29, 115.33 (Ar-CH), 66.53
(OCH2), 52.93 (OCH3), 39.23, 37.27, 36.10, 24.66 (CH2), 29.83, 27.98
(CH), 22.71, 22.61, 19.65 (CH3). C23H31NO3 MW: 369.50 g/mol. Full
MS ESI (electrospray ionization) (þ) [50.00e1000.00]: 370 (80)
rotation: ½
a
ꢃ
¼ ꢁ0.137ꢀ (c ¼ 1 mg/mL in CHCl3 at 20 ꢀC).
3. Results and discussion
[Mþ], 310 (66) [Mþ-C2H3O2],170 (100) [C11H8NO]. Optical rotation:
20
589
¼ ꢁ0.099ꢀ (c ¼ 1 mg/mL in CHCl3 at 20 ꢀC).
3.1. Mesomorphic properties
½a
ꢃ
The mesomorphic properties of the pyridine-based methyl es-
ters (3a-e) with different terminal chains were investigated by
using optical polarizing microscope (PM) and differential scanning
calorimeter (DSC). The mesophase type, transition temperatures (T,
2.2.6. Methyl 5-(4-(3,7-dimethyloctyloxy)phenyl)pyridine-2-
carboxylate (3e)
Yield: 80%; 0.222 g; colorless crystals. 1H-NMR (500 MHz,
CDCl3):
d
(ppm) ¼ 8.95 (dd, J z 2.3 Hz and 0.6 Hz, Pyridine Ar-H),
in degree Celsius) and the corresponding enthalpies (DH, in kJ
8.19 (dd, J z 8.2 Hz and 0.6 Hz, Pyridine Ar-H), 7.99 (dd, J z 8.2 Hz
and 2.3 Hz, Pyridine Ar-H), 7.58 (d, J z 8.8 Hz, 2 Ar-H), 7.04 (d,
J z 8.8 Hz, 2 Ar-H), 4.10e4.04 (m, 5H, OCH2 ve OCH3), 1.90e1.84 (m,
1H, CH), 1.74e1.68 (m, 1H, CH), 1.66e1.51, 1.39e1.15 (2m, 8H, 4 CH2),
0.97 (d, J z 6.6 Hz, 3H, CH3), 0.89 (d, J z 6.5 Hz, 6H, 2 CH3). 13C-
molꢁ1) of 3a-e are presented in Fig. 1.
New pyridine-based methyl esters 3a, 3b and 3c carrying a n-
alkyloxy chain with n ¼ 8, 10 and 12 exhibit enantiotropic smectic A
mesophase which is characterized by the typical fan-shaped
texture of calamitic shaped molecules (see Figs. 1 and 2).
NMR (125 MHz, CDCl3):
d
(ppm) ¼ 165.74 (CO), 160.04, 145.66,
The differential thermograms of 3a and 3b show three endo-
therms for a phase transition sequence of crystal (Cr1) - crystal (Cr2)
- smectic A (SmA) - isotropic phase (iso) on heating and two exo-
therms for a phase transition sequence of isotropic phase (iso) -
139.49, 128.64 (Ar-C), 147.81, 134.35, 128.48, 125.24, 115.31 (Ar-CH),
66.53 (OCH2), 52.89 (OCH3), 39.23, 37.27, 36.10, 24.66 (CH2), 29.83,
27.98 (CH), 22.71, 22.61, 19.65 (CH3). C23H31NO3 MW: 369.50 g/mol.
Fig. 1. Mesophase, transition temperatures and corresponding transition enthalpies of the compounds 3a-e.

G. Karanlık et al. / Journal of Molecular Structure 1198 (2019) 126930
5
Fig. 2. DSC thermograms (a,c,e) on 2nd heating and cooling (10 ꢀC minꢁ1) and fan-shaped textures of SmA mesophase of compound 3a-c as observed between crossed polarizers
(indicated by arrows) in a nontreated microscopic glass slides on cooling; (b) compound 3a at T ¼ 105.0 ꢀC, (d) compound 3b at T ¼ 109.0 ꢀC and (f) compound 3c at T ¼ 110.0 ꢀC and
the inset corresponds to helical strands obtained by stressing a homeotropic texture of the SmA mesophase during heating at 115 ꢀC.
smectic A (SmA) - crystal (Cr) on cooling. The melting point of
compound 3b is higher about 5 ꢀC than 3a whereas the clearing
points are the same of both compounds. Compound 3c carrying an
n-dodecyloxy terminal chain, exhibits same mesophase as
observed for compounds 3a and 3b carrying an alkyl chain with
lower numbers of carbon atoms. In addition to crystal e crystal
transitions on heating were not observed, phase transition tem-
peratures decreased about 3 ꢀC as compared to those of compounds
3a and 3b depending on the increase on the alkyloxy chain length
(see Figs. 2 and 4).
Compound 3d and 3e, which have a 3,7-dimethyloctyloxy
branched chain in chiral and racemic form respectively, show
enantiotropic smectic A phase which is identified with fan-shaped
texture which is in agreement with the texture observed for anal-
ogous pyridine-based esters 3a, 3b and 3c with straight alkyloxy
chain (see Figs. 1 and 3). One striking point here for compounds 3d
and 3e as mentioned compounds for branched chains [39] that the
introducing of a branched chain instead of a straight chain at

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G. Karanlık et al. / Journal of Molecular Structure 1198 (2019) 126930
Fig. 3. DSC thermograms (a [38], c) on 1st heating and cooling (10 ꢀC minꢁ1) and fan-shaped textures of SmA mesophase of compound 3d and 3e as observed between crossed
polarizers (indicated by arrows) in a 5
m
m PI non-coated ITO cell on cooling; (b) compound 3d at T ¼ 60.0 ꢀC and focal conic texture of the SmA phase between microscopic glass
slides at T ¼ 87 ꢀC on heating, (d) compound 3e at T ¼ 60.0 ꢀC.
terminal gives rise to a significant decrease about 30.0 ꢀC in clearing
points. Additionally, the mesophase temperature range of smectic A
(Sm A) mesophase existing over 50 ꢀC which is broader as
compared to compounds 3a-c depending on sharply decrease on
crystallization temperature. Both compounds show a transition to
crystal around 30 ꢀC on cooling (see Figs. 3 and 4).
and racemic form behave in regard to mesogenity similarly. They
show the same LC phase with almost the same transition temper-
atures. However, compound 3e exhibits
a phase transition
sequence of Cr1eCr2-SmAeIso which are in agreement with three
endotherms on heating curves. The transition peaks from the
isotropic liquid to the SmA phase and vice versa are broad as well as
melting point is sharply lower than that of chiral counterpart 3d
Compounds 3d and 3e with branched terminal chain in chiral
Fig. 4. Comparison of the liquid crystalline behavior of the new pyridine-based methyl esters (3a-e) on cooling.

G. Karanlık et al. / Journal of Molecular Structure 1198 (2019) 126930
7
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acterization of a new pyridine-based methyl esters 3a-e carrying a
n-alkoxy chain or 3,7-Dimethyloctyloxy branched group at termi-
nal have been reported. The compounds 3a-e show an enantio-
tropic smectic A phase with a fan-shaped texture at a variable
mesomorphic range depending on alkoxy chain length and
branching at terminal. The increase on an alkoxy chain length gives
rise to a slight decrease on transition temperatures whereas the
positioning of a branched chain to terminal results in a sharply
change on mesomorphic transitions with preserving mesophase
type. The comparison with branched analogs 3d and 3e with a
straight chain analog carrying the same number of carbon atoms
shows that an increase up to 50 ꢀC occurs in the mesophase in-
tervals by the effect of a chain branching at terminal. Compound 3d
and 3e with 3,7-Dimethyloctyloxy branched chain in chiral and
racemic form exhibit same mesophase in the same order with
almost the same transition temperatures. As known, the intro-
duction of a chiral unit into the terminals of calamitic mesogens
results in the occurrence of chiral mesophases. However, no po-
larization peak was observed for compound 3d in spite of the
presence of a chiral moiety. It can be noted here as a main point that
the degree of optical purity for a compound carrying a chiral moiety
can play a considerable role on the occurrence of chiral mesophases
depending on mesogenic structure. This study will be continued on
a detailed investigation of dielectric properties and ac conductivity
mechanism of these LCs.
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Acknowledgements
This research has been supported by The Scientific and Tech-
_
nological Research Council of Turkey (TÜBITAK), Turkey with the
Project Number 116Z465.
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Appendix A. Supplementary data
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