Multichiral liquid crystals based on terphenyl core laterally substituted by chlorine atom

Article abstract of DOI:10.1016/j.molliq.2021.116267

We designed a new type of antiferroelectric liquid crystalline structure with versatile properties. For this purpose, we modified the previously studied liquid crystalline compounds based on terphenyl molecular core laterally substituted with a chlorine atom. Two lactate units were attached to the chiral chain with the aim to support antiferroelectric structures. We studied the mesomorphic properties of new compounds by means of texture observations under a polarised light microscope, by dielectric spectroscopy and electro-optical measurements. To confirm the phase identification, x-ray measurements were performed. We found that the studied compounds revealed a SmA*-SmC* phase sequence in a broad temperature range. We proved an antiferroelectric phase with orthoconic properties for selected structural modifications. Such valuable optical properties with the tilt angle about 45° promise a big potential for applications.

Full text of DOI:10.1016/j.molliq.2021.116267

Journal of Molecular Liquids 336 (2021) 116267
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Multichiral liquid crystals based on terphenyl core laterally substituted
by chlorine atom
a
a
a
b
a,
⇑
ˇ
Natalia Podoliak , Martin Cigl , Vera Hamplová , Damian Pociecha , Vladimíra Novotná
a Institute of Physics of the Czech Academy of Sciences, Na Slovance 2, Prague, Czech Republic
b Faculty of Chemistry, University of Warsaw, Al. Zwirki i Wigury 101, Warsaw, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
We designed a new type of antiferroelectric liquid crystalline structure with versatile properties. For this
purpose, we modified the previously studied liquid crystalline compounds based on terphenyl molecular
core laterally substituted with a chlorine atom. Two lactate units were attached to the chiral chain with
the aim to support antiferroelectric structures. We studied the mesomorphic properties of new com-
pounds by means of texture observations under a polarised light microscope, by dielectric spectroscopy
and electro-optical measurements. To confirm the phase identification, x-ray measurements were per-
formed. We found that the studied compounds revealed a SmA*-SmC* phase sequence in a broad temper-
ature range. We proved an antiferroelectric phase with orthoconic properties for selected structural
modifications. Such valuable optical properties with the tilt angle about 45° promise a big potential for
applications.
Received 1 March 2021
Revised 14 April 2021
Accepted 20 April 2021
Available online 24 April 2021
Keywords:
Terphenyl
Lactate
Chlorine lateral substitution
Orthoconic
Ó 2021 Elsevier B.V. All rights reserved.
Antiferroelectric
1. Introduction
has been the application of fluorine at various positions; in this
case the selected derivatives have demonstrated the orthoconic
Ferroelectric and antiferroelectric properties in liquid crystals
(LCs) are attracting attention of scientists due to their potential
in modern technology [1]. Such a type of materials was expected
to replace nematics due to a faster response-time and more-
functional operation regime. Besides display applications, LCs can
be useful for laser beam steering and spatial modulators. From
the discovery of antiferroelectric liquid crystals [2], an intensive
effort was devoted to the designing of new compounds and
improving their electro-optical properties with the aim to prepare
versatile materials for future applications.
Within the diverse strategies to synthesise new LC compounds,
chemists vary a molecular core, linking groups and terminal
chains. Mesogenic molecules containing several aromatic rings in
their core often evinced broader temperature ranges of meso-
phases in comparison with shorter ones. On the other hand, such
compounds revealed rather high transition temperatures, which
imposed restrictions on their application [3]. Terphenyl molecular
core has been previously utilised and such compounds have
revealed high birefringence [4–6], which has been positively
reflected in photonic applications. To lower the clearing point of
terphenyl materials and increase the birefringence, a variety of
lateral substitutions have been applied [7–10]. The most often
properties [9,10]. Polar lateral substituents were used to obtain
nematic terphenyl materials with negative dielectric anisotropy
for vertically aligned mode in display technologies [11]. Addition-
ally, the terphenyl molecular core was synthesised as a chiral host
for ferroelectric mixtures preparation [12]. Later such a molecular
core has been repeatedly applied for the design of chiral LC com-
pounds. Recently, a systematic study describing the effect of the
terminal chains on the formation of smectic or nematic phases in
this type of materials has been published [13–17].
In our previous research of chiral compounds, we often utilised
the lactate unit as a source of chirality. We have reported a great
number of chiral compounds with a broad variety of mesophases,
including cholesteric, TGB and Blue Phases [18–22]. To support
the formation of the smectic phases, we have concentrated on a
four-ring molecular core based on two biphenyls laterally substi-
tuted with a chlorine atom [21–24]. We have applied a chlorine
substitution at different positions to suppress the transition tem-
peratures, which are typically high for such a big molecular core,
and reached an effective decrease in temperatures [21–24]. There
are tendencies to apply more than one chiral centre with the aim
to support the chirality. Nevertheless, the effect of multichiral ter-
minal chain is not properly described and explained. In several
cases the chirality has been introduced in the form of two chiral
moieties located at both peripheral ends and such compounds have
been reported to show the antiferro-, ferri-, and ferroelectric
⇑
Corresponding author.
E-mail address: novotna@fzu.cz (V. Novotná).
https://doi.org/10.1016/j.molliq.2021.116267
0167-7322/Ó 2021 Elsevier B.V. All rights reserved.

ˇ
N. Podoliak, M. Cigl, Vera Hamplová et al.
Journal of Molecular Liquids 336 (2021) 116267
phases [25,26]. Another way to increase the chirality effect is to
multiply the chiral centres in the chain, which in several cases
has induced a rich polymorphism including antiferroelectricity
[27–33].
covered with ITO (indium tin oxide) transparent electrodes and a
polymer coating, which ensured a planar uniform homogeneous
(HG) geometry. We determined the sequences of phases and the
phase transition temperatures from the characteristic textures
and their changes, observed in polarised light optical microscope
(POM) during the sample cooling. For this purpose, we used the
microscope Nikon eclipse E600 pol (Nikon, Tokyo, Japan), equipped
with Canon EOS 700D photo camera and Linkam LTSE350 (Linkam,
Tadworth, UK) heating stage, with the temperature
stabilisation 0.1 K, for the temperature control. The precise phase
transition temperatures were obtained from the differential scan-
ning calorimetry (DSC) using Perkin-Elmer DSC 8000 calorimeter
(Pyris Diamond Perkin Elmer, Shelton, CT, USA). For these measure-
ments, 1–3 mg samples were hermetically sealed into aluminium
pans and placed into the calorimeter chamber filled with nitrogen.
From the dielectric spectroscopy measurements, the complex
We presented chiral liquid crystalline materials with the molec-
ular core consisted of chlorine laterally-substituted terphenyl con-
nected via ester linkage with a phenyl ring, with lactate and
methylbutyl in the chiral terminal chain [34]. We observed a
SmA-SmC* phase sequence in extremely broad temperature range
and detected high polarisation values as well as a high tilt angle up
to 42°. We believe that those derivatives represented a promising
type of smectogens and supplied a pool for new smart materials.
Herein, we present analogous terphenyl derivatives, with the same
molecular core, which was studied previously in Ref. [34]. We pre-
pared and studied a new series with two lactate units and/or addi-
tional methylbutyl in the chiral chain. General chemical formula of
the compounds, denoted TLLn/6 and TLL10/*, is presented in Fig. 1.
For the presented compounds TLLn/6, we pursued the effect of the
terminal alkyl length on the mesomorphic properties with the aim
to compare the studied derivatives with analogous compounds
[34] and to establish the role of the additional lactate unit in the
chiral chain. For this study, we applied various experimental tech-
niques such as differential scanning calorimetry (DSC), polarising
optical microscopy (POM), dielectric spectroscopy, spontaneous tilt
angle and polarisation measurements to describe the mesomor-
phic properties. Additionally, X-ray diffraction (XRD) measure-
ments were performed to confirm the mesophase identification.
permittivity (e*) was obtained utilising Schlumberger 1260 impe-
dance analyser (Schlumberger, Houston, TX, USA). The resistance
and capacity were detected in the frequency range 10–106 Hz dur-
ing the sample cooling. The real, e0, and imaginary, e00, parts of the
complex permittivity e
*(f) = e0-ie00 were were simultaneously fitted
as functions of frequency at a selected temperature to the gener-
alised Cole-Cole formula:
ꢂ
ꢃ
D
e
f
r
2pe
eꢀ
ꢁ
e1
¼
Þ ꢁ i
þ Afn
ð1Þ
ꢀ
ꢁð1ꢁ
0fm
a
i
fr
1 þ
where fr is the relaxation frequency, 4
e
the dielectric strength,
a
2. Experimental
the distribution parameter of relaxation,
e
0 the permittivity of vac-
uum, e1 the high frequency permittivity; m, n, A are the parameters
of fitting. The second and the third terms in (1) are added to elim-
2.1. Synthesis
inate the contribution of d.c. conductivity,
the contribution of the ITO electrodes resistance at high frequen-
cies, respectively.
r, at low frequencies and
The studied materials were synthesised according to Scheme 1.
The synthesis of
a
chiral part started from methyl 4-
hydroxybenzoate (1), which was reacted with benzyl chloride to
protect the hydroxy group and, subsequently, the ester moiety
was hydrolysed to liberate the protected benzoic acid 2. In the next
step, the acid 2 was treated with oxalyl chloride giving benzoyl
chloride 3, which was utilised for the connection of the chiral ali-
phatic part in the reaction with the chiral ester 4 or 4b, synthesised
as described in Ref. [33]. After that, the hydroxyl groups of the
obtained chiral esters 5a and 5b were liberated by means of
hydrogenolysis to yield chiral phenols 6a and 6b, respectively. Ter-
phenylcarboxylic acids 7/n (n = 8–10) with C8-C10 alkyl chains
were synthesised according to the previously reported procedure
[34] and reacted with the chiral phenol 6 in the DCC-mediated
reaction, giving target mesogenic materials TLL n/6. Material
TLL10/* was synthesised via the same reaction using the ter-
phenylcarboxylic acid 7/10 and the chiral phenol 6b.
The spontaneous polarisation, Ps, was measured by the integra-
tion of the polarisation current peak, detected during the switching
under a triangle a.c. field of the amplitude about 3.5 V/lm and the
frequency 10 Hz, applied to the sample. The spontaneous tilt angle,
Hs, was determined optically from the difference between the
extinction positions under the opposite d.c. electric fields 4 V/
l
m using crossed polarisers. The pitch of the SmC* helical structure,
p, was determined from the light diffraction on the dechiralization
lines. For this experiment we utilised 50 mm thick glass cells to
minimise the influence of the surfaces on the helical structure.
The X-ray diffraction measurements were performed to deter-
mine the structural properties of the mesophases. To obtain tem-
perature evolution of smectic layer spacing we used Bruker D8
Discover (Bruker AXS, Karlsruhe, Germany) diffractometer (CuK
a
radiation, parabolic mirror monochromator, scintillation counter),
equipped with Anton Paar DCS-350 heating stage (Anton Paar,
Graz, Austria) with the temperature stabilization 0.1 K for the
temperature control. The samples were prepared as thin films on
a heated surface and the measurements were conducted in the
2.2. Experimental set-up and measurements
For the optical and electrooptical studies, the commercial glass
cells of thicknesses 7 and 12
lm, provided by AWAT company
reflection mode. Bruker GADDS system (CuK radiation, parabolic
a
(AWAT, Warsaw, Poland), were filled with synthesised materials
in the isotropic phase by capillary action. The cells surfaces were
mirror monochromator, point beam collimator, Vantec 2000 area
detector) equipped with modified Linkam heating stage was used
for the broad-angle XRD studies. Partially oriented samples for
the experiments were prepared as droplets on a heated surface.
3. Results and discussion
3.1. Mesomorphic behaviour
All studied compounds, prepared according to the procedures
described above, were subjected to calorimetric measurements.
Fig. 1. Chemical formula of the studied LC series TLLn/6, n = 8–10.
2

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N. Podoliak, M. Cigl, Vera Hamplová et al.
Journal of Molecular Liquids 336 (2021) 116267
Scheme 1. The synthesis of the target materials with two lactate units.
From the DSC measurements, we established the onset tempera-
tures of the phase transitions and the corresponding enthalpy
changes. The obtained data are summarised in Table 1. For all three
compounds TLLn/6, the melting points were detected only for the
first heating run and we did not observe any crystallisation. For
TLL10/*, the second DSC temperature run is demonstrated in
Fig. 2. The crystallisation for TLL10/* did not appear on cooling,
but during the subsequent heating (in red colour) as an opposite
peak (exothermic instead of endothermic). Such a type of beha-
viour and a postponed crystallisation has been previously reported
for various lactic acid derivatives [18,23]. It is necessary to point
out that we did not observe any crystallisation for TLLn/6 and
the melting points in Table 1 were taken from the first DSC heating
runs. All studied compounds revealed a glassy behaviour below
0 °C, as it is presented for TLL10/* in Fig. 2.
3.2. SmA*-SmC* phase sequence for TLLn/6 compounds
Fig. 2. DSC plot for TLL10/*. The phases are marked, the red and blue colours
correspond to the heating and cooling runs, resp.
From the textures observed under a polarising microscope and
electro-optical properties, studied for all compounds, TLLn/6 pos-
sessed a SmA*-SmC* phase sequence with the first order phase
transition between the paraelectric and ferroelectric phases. Both
mesophases existed in a broad temperature range and the ferro-
electric SmC* phase persisted to the room temperature while cool-
ing. In planar cells, TLLn/6 compounds showed fan-shaped textures
Table 1
The phase transition temperatures, Ttr, the temperatures of the isotropic-mesophase transition, Tiso, and the melting points, m.p., taken during the second DSC runs. Temperatures
are in °C and the corresponding enthalpy changes, 4H, in kJ/mol, are in brackets at the corresponding temperatures. The symbol & means that the phase exists and the symbol –
that the phase does not exist, ? symbolises that the phase was not unambiguously identified.
Material
m.p.
SmCA*
Ttr [4H]
SmC*
Ttr [4H]
SmA*
Tiso [4H]
TLL8/6
TLL9/6
TLL10/6
TLL10/*
44 [+14.1]
40 [+6.47]
45 [+21.4]
44 [+6.48]
?
?
?
&
25
20
21
&
&
&
&
113 [ꢁ0.07]
118 [ꢁ0.09]
116 [ꢁ0.52]
&
&
&
–
170 [ꢁ2.15]
175 [ꢁ1.47]
168 [ꢁ1.70]
98 [ꢁ10.5]
77 [ꢁ0.27]
3

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N. Podoliak, M. Cigl, Vera Hamplová et al.
Journal of Molecular Liquids 336 (2021) 116267
and an array of dechiralization lines appeared at the transition to
the SmC* phase. The typical microphotographs of the textures
are presented in Fig. 3a and b for TLL8/6, in the SmA* and SmC*
phases, respectively. For TLL10/6, the textures are in Supplemental
file, Fig. S1.
During the light diffraction experiments, the incident He-Ne
laser light diffracted on the regular array of the dechiralization
lines. We were able to detect the diffraction circles on the screen
and to measure the pitch length, p. For TLL9/6 and TLL8/6, the tem-
perature dependences of p(T) are presented in Supplemental file, in
Fig. S2. The pitch length grew below the SmA*-SmC* phase transi-
tion, saturated and slightly fell down with lowering temperature.
The values of the pitch varied from 900 nm to 1.4
and from 1.4 m. to 1.7 m for TLL9/6. For TLL10/6 we were not
able to measure the pitch by this method and we expect that the
pitch values might be lower than 1 m.
lm for TLL8/6
l
l
l
The temperature dependence of the spontaneous polarisation,
Ps(T), measured within the SmC* phase, is shown in Fig. 4a for all
TLLn/6 compounds. The polarisation values increased up to 130
nC/cm2. Unfortunately, the viscosity grew with the samples cool-
ing and below 50 °C we were not able to switch the sample by a.
c. electric field. The temperature dependences of the tilt angle,
Hs, are presented for TLLn/6 in Fig. 4b. The tilt angle showed a
jump at the SmA*-SmC* transition temperature and grew very
steeply.
H values increased up to 45° with cooling down to the
room temperature.
Dielectric spectroscopy can give us relevant information about
collective or individual molecular relaxation processes in liquid
crystals. We performed dielectric measurements for all mesogens
TLLn/6. The dielectric behaviour was very similar for all three
homologues. To illustrate the raw data, we present
a 3-
dimensional graph for the real and imaginary parts of the permit-
tivity in Fig. 5 for TLL8/6. We simultaneously fitted the measured
Fig. 4. Temperature dependence of: (a) the spontaneous polarisation, Ps; (b) the
spontaneous tilt angle,
Hs, for TLLn/6 series.
real, e’, and imaginary, e’’, parts of the permittivity to the Cole-
Cole formula (1). The results of the fitting are shown for TLLn/6
in Fig. 6. We detected a weak relaxation mode in the SmA* phase,
the dielectric strength, 4
e, of which increased with the sample
cooling and the relaxation frequency, fr, softened when approach-
ing the SmA*-SmC* phase transition. At the SmC* phase, another
relaxation mode appeared, with rather high values of 4
e, which
can be attributed to the Goldstone mode. It is necessary to point
out that at the SmA*-SmC* phase transition there were narrow
temperature intervals (1-1.5°C), in which the soft and the Gold-
stone mode coexisted due to the first order character of the phase
transition and the permittivity fitting was problematic. One can see
the permittivity frequency-dependences at the SmA*-SmC* phase
transition temperature, Tc, for TLL10/6 in Supplemental file
(Fig. S3). Such a profile evidences the presence of more than only
one relaxation process at the vicinity of Tc. On the cooling process
within the SmC* phase, we observed one distinct mode. Neverthe-
less, the distribution parameter,
a, was rather high (
a
ꢂ0.2-0.25) in
the temperature interval 10-15°C below Tc. We found the relax-
ation frequency, fr(T) was slightly increasing and then started to
decrease at temperatures below Tc-15ºC on the sample cooling
within the SmC* phase. Such non-monotonous behaviour of fr(T)
can be explained with the presence of parasitic surface layers
due to rather high contribution of the ionic low-frequency conduc-
tivity. On the cooling process, the ionic conductivity decreased and
the viscosity increased, which surely influenced the relaxation
dynamics and the temperature profile of the Goldstone mode.
Fig. 3. Textures of TLL8/6 compound in (a) the SmA* phase; (b) the SmC* phase
under the polarising microscope. The width of the photos is about 200 lm.
4

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N. Podoliak, M. Cigl, Vera Hamplová et al.
Journal of Molecular Liquids 336 (2021) 116267
Fig. 6. Fitted values of (a) relaxation frequencies, fr, and (b) dielectric strength, De,
for TLLn/6 materials. The areas of the soft mode and the Goldstone mode
contribution are interupted with the dotted lines.
high-angle range evidencing the absence of the long-range correla-
tions of molecular positions within the smectic layers. Such pat-
terns are characteristic for liquid-like smectic phases, SmA and
SmC. From the positions of the small-angle peaks, we have calcu-
lated the layer spacing, d, as a function of temperature for all
TLLn/6 homologues (Fig. 7). Comparing the measured d values in
the SmC* phase with the extrapolated linearly d(T) dependence
in the SmA*, it was possible to determine the tilt angle value. Inset
in Fig. 7 shows a comparison of the temperature dependence of the
tilt angle measured optically, Hs, and obtained from x-ray diffrac-
tion data, Hx, for TLL9/6. For homologues TLL8/6 and TLL10/6, the
temperature dependences of the tilt values Hs, and Hx are shown
in Supplemental file (Fig. S4). In all cases, optical measurements
yielded higher values of the tilt angle. Additionally, it should be
noted that the calculated molecular lengths for the most extended
molecular conformation, 47.2 Å and 48.5 Å for TLL9/6 and TLL10/6,
respectively, were much higher than the layer spacing measured in
the SmA* phase. It is evident that the studied molecules could not
exist in the most extended molecular conformations in meso-
phases, their chains must be surely entangled. This assumption
will be analysed later in Discussion.
Fig. 5. Dielectric spectroscopy data for TLL8/6 homologue: (a) real, e0, and (b)
imaginary, e00, parts of dielectric permittivity in dependence of frequency and
temperature, T.
As it was pointed out above, we did not gain any clear evidence
of crystallisation during the sample cooling. For the overcooled
TLLn/6 samples, at a temperature 20–25 °C, we observed a change
in planar textures and measured a clear decrease of permittivity. In
the permittivity measurements at temperatures below 20ºC, we
detected a weak high-frequency mode, which can be attributed
to the anti-phase mode, characteristic for antiferroelectric phase,
or to the molecular mode. Frequency profile of permittivity at
lower temperatures is presented for TLL8/6 and TLL9/6 in Supple-
mental file (Fig. S3). Unfortunately, we have no more evidence that
the antiferroelectric SmCA* phase for TLLn/6 is really present, we
can only speculate.
We performed X-ray diffraction study to establish the meso-
phase structural parameters and to prove the phase identification.
Recorded XRD patterns showed series of sharp, commensurate
signals in the small-angle region, which are due to the lamellar
organization of molecules, and a broad diffuse maximum in the
3.3. Antiferroelectric phase in TLL10/*
On contrary to TLLn/6 compounds, homologue TLL10/* exhib-
ited a direct phase transition from the isotropic phase (Iso) to the
ferroelectric SmC* phase. The planar textures for TLL10/* revealed
5

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N. Podoliak, M. Cigl, Vera Hamplová et al.
Journal of Molecular Liquids 336 (2021) 116267
Fig. 7. Temperature dependences of the layer spacing value, d, calculated from the
x-ray diffraction data, for TLLn/6 compounds. In the inset, the temperature
dependence of the tilt angle measured optically for TLL9/6, Hs, and recalculated
from extrapolated d(T) measured within the SmA* phase, Hx, are presented.
a broken fan-shaped texture in the SmC* phase. We did not observe
regular arrays of dechiralization lines and from the behaviour in
applied electric field we considered that the pitch is probably
lower than 1 lm. The growth of the SmC* nuclei in planar geome-
try is shown in Fig. S5 in Supplemental file. The fan-shaped texture
changed at a temperature about 77 °C, which we attributed to the
SmC*-SmCA* phase transition. This phase transition was evident in
free-standing films as well, when a schlieren texture of the SmC*
phase was replaced by another one. Schlieren textures of both
mesophases are demonstrated in Supplemental file, Fig. S6.
As well as for the previous compounds, we measured polarisa-
tion, Ps, by the integration of the switching current peak for TLL10/
*. The polarisation steeply jumped up at the Iso-SmC* phase tran-
sition and was increasing with the sample cooling. There was no
distinct anomaly in the Ps(T) dependence at the SmC*-SmCA* phase
transition, as it is demonstrated in Fig. 8a. On the other hand, the
response time and the coercive field of the switching started to
increase at the SmC*-SmCA* phase transition. Within the antiferro-
electric SmCA* phase, the switching time continuously grew on
cooling and at temperatures below T = 40 °C we were not able to
measure any polarisation at frequency 50 Hz. In Fig. 8b, we present
the profile of the switching current at several temperatures in both
mesophases for comparison. The tilt angle, Hs, measured for
TLL10/*, exhibited very high values about 40° just below the Iso-
SmC* phase transition. Within the SmC* and SmCA* phases, Hs
grew and saturated at a value about 45°, no anomaly at the
SmC*-SmCA* phase transition was found.
Fig. 8. For homologue TLL10/*: (a) temperature dependence of the spontaneous
polarisation, Ps, and tilt angle, Hs; (b) the polarisation current profiles at selected
temperatures at a frequency 50 Hz. The temperatures were selected for demon-
stration at T = 90 °C in the SmC* phase, at T = 70 °C and T = 50 °C in the SmCA* phase.
plotted the frequency dependences of e’’ at selected temperatures
in the SmCA* phase to demonstrate this high-frequency mode.
The complex analysis of the mesomorphic behavior for TLL10/*
was accomplished with X-ray diffraction measurements. For both
mesophases, only commensurate sharp signals were found in the
small-angle region of the XRD patterns and a broad high-angle
maximum, pointing to the liquid-like character of the molecular
packing within the layers (Fig. 11). Such data demonstrate the
smectic character of both mesophases and the absence of the addi-
tional ordering within the layers. The smectic layer thickness, d,
decreases monotonically on cooling, with small anomaly at the
SmC*- SmCA* phase transition; the transition is also accompanied
with small step increase of diffraction signal intensity, but no qual-
itative change in the diffraction pattern was found.
We performed the dielectric spectroscopy measurements to
testify the phase identification. The study of the relaxation pro-
cesses is useful in the determination and classification of various
chiral smectic phases. As it is typical for a ferroelectric mesophase,
we observed a strong low-frequency mode in the SmC* phase. The
complete set of measured dielectric data for TLL10/* is shown in
Fig. 9. In the SmC* phase, the strong Goldstone mode was found
and fitted to formula (1). The results of the fitting, namely, the val-
4. Discussion and conclusions
In the present study, we prepared new lactate derivatives based
on terphenyl molecular core laterally substituted with a chlorine
atom. We modified the previously studied structure [34] and
added one more lactate group into the terminal chiral chain. For
homologues TLLn/6 with two lactates in the chain, we detected
the SmA*-SmC* phase sequence in a broad range of temperatures.
Studied compounds did not crystallise, nevertheless, their viscosi-
ties at the room temperature are rather high. At lower tempera-
tures below 25 °C, we detected a liquid crystalline phase, which
exhibited a dielectric response characteristic for antiferroelectric
ues of the dielectric strength, 4
are deposited in Supplemental file (Fig. S7). We obtained very high
values of 4 reaching up to 600; the relaxation frequency was con-
tinuously decreasing with lowering temperature. In Fig. 10, we
plotted the temperature dependences of the real, ’, and imaginary,
’’, parts of the permittivity at 1 kHz to demonstrate the drop down
e, and the relaxation frequency, fr,
e
e
e
of the permittivity at the SmC*-SmCA* phase transition. In the anti-
ferroelectric SmCA* phase, only very weak mode was detected,
with a decreasing relaxation frequency. In the inset of Fig. 10, we
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N. Podoliak, M. Cigl, Vera Hamplová et al.
Journal of Molecular Liquids 336 (2021) 116267
Fig. 10. Temperature dependences of the real, e0, and imaginary, e00, parts of the
permittivity at 1 kHz for TLL10/*. In the inset, there are the frequency dependences
of e00 at selected temperatures: 75 °C, 50 °C and 35 °C in the antiferroelectric SmCA*
phase.
Fig. 9. Dielectric spectroscopy data for TLL10/* homologue: (a) real, e0, and (b)
imaginary, e00, parts of dielectric permittivity in dependence of frequency and
temperature, T.
phase. We did not observe any phase transition below 25 °C during
DSC measurements, nevertheless, the enthalpy of the SmC*- SmCA*
phase transition can be very small. We obtained only limited infor-
mation about this mesophase and we cannot unambiguously
establish its character. We only speculate that an antiferroelectric
mesophase might exist for TLLn/6 compounds below 25 °C.
During the previous studies of the lactate derivatives [20,21],
we found that the presence of an additional lactate group in the
chiral chain decreased the mesophase transition temperatures
[27–32]. Concerning a change of the isotropic-mesophase transi-
tion temperature, Tiso, we obtained only a decrease for 5–10 °C in
comparison with terphenyl analogous derivatives possessing one
lactate in the chiral chain [34]. It was less than we observed for
other types of compounds with four-ring molecular core laterally
Fig. 11. The X-ray results for TLL10/*: (a) the intensity profile in a broad range of
scattering angles, 2h, at two selected temperatures (at T = 90 °C in the SmC* phase
and at T = 60 °C in the SmCA* phase). In the inset in the right upper corner, there is a
2D diffraction pattern of a partially aligned sample in the SmCA* phase at the
temperature T = 60 °C. (b) temperature dependences of the layer spacing, d, and the
intensity, Int., of the corresponding XRD signal.
7

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N. Podoliak, M. Cigl, Vera Hamplová et al.
Journal of Molecular Liquids 336 (2021) 116267
pean Structural and Investment Funds [project SOLID21-CZ.02.1.
01/0.0/0.0/16_019/0000760.
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
Appendix A. Supplementary material
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.molliq.2021.116267.
References
Fig. 12. Molecular conformations calculated for TLL10/6: (a) in the most extended
molecular shape and (b) with an entangled chain.
[1] J.W. Goodby, R. Blinc, N.A. Clark, S.T. Lagerwall, M.A. Osipov, S.A. Pikin, T.
Sakurai, K. Yoshino, B. Zeks, Ferroelectric liquid crystals: Principles, properties
and applications, Gordon and Breach Science Publishers, Philadelphia, 1991.
[2] A.D.L. Chandani, E. Gorecka, Y. Ouchi, H. Takezoe, A. Fukuda, Antiferroelectric
Chiral smectic phases responsible for the tristable switching in MHPOBC, Jpn. J.
Appl. Phys. 28 (1989), L1265–L1265.
[3] H.A. Ahmed, G.R. Saad, Mesophase behaviour of laterally di-fluorosubstituted
four-ring compounds, Liq. Cryst. 42 (2015) 1765–1772.
[4] G.W. Gray, D.G. McDonnell, Synthesis and liquid-crystal properties of chiral
alkyl-cyano-biphenyl (and alkyl-cyano-p-terphenyls) and of some related
chiral compounds derived from biphenyl, Mol. Cryst. Liq. Cryst. 37 (1976) 189–
211.
[5] R. Dabrowski, J. Dziaduszek, A. Ziolek, L. Szczucinski, Z. Stolarz, G. Sasnouski, V.
Bezborodov, W. Lapanik, S. Gauza, S.T. Wu, Low viscosity, high birefringence
liquid crystalline compounds and mixtures, Opto-Electro. Rev. 15 (2007) 47–
51.
[6] G.W. Skelton, P. Brett, J.C. Jones, S.M. Kelly, V. Minter, R.P. Tuffin, Terminal
trifluoromethyl-alkoxy and –alkenyloxy nematic liquid crystals for LCDs with
active matrix addressing, Liq. Cryst. 28 (2001) 417–435.
[7] M.J. Goulding, S. Greenfield, Mesomorphic properties of some laterally
fluorinated 4-alkyl,4’’-oxoalkyl 1,1’:4’,1’’ terphenyls, Liq. Cryst. 13 (1993)
345–351.
[8] G.W. Gray, M. Hird, D. Lacey, K.J. Toyne, The synthesis and transition
temperatures of some 4,4‘‘-dialkyl- and 4,4”-alkoxyalkyl-1,1’:4’,1‘‘-terphenyls
with 2,3- or 2’,3’-difluoro substituents and of their biphenyl analogues, J.
Chem. Soc., Perkin Trans. 12 (1989) 2041–2053.
substituted with a chlorine atom [20], for which we detected a
decreasing of all phase transition temperatures by at least 15 °C.
The transition temperatures for TLLn/6 did not vary monotonously
with the prolongation of the non-chiral chain length (with increas-
ing n number). Additionally, the layer spacing in the SmA phase did
not increase with n in a monotonous way, as for the longest homo-
logue TLL10/6 we monitored the drop down of d in comparison
with TLL9/6. We can conclude that the molecular chains were more
entangled when prolonging their length. All these findings were
fully consistent with the molecular models: we modelled several
molecular conformations, in which the molecular length substan-
tially differed (Fig. 12). In the most extended conformation, the
molecular length, l, for TLL10/6 was established to be about
48.5 Å (Fig. 12a). On the other hand, the optimised model of a con-
formation with the entangled chiral chain (Fig. 12b) gave the
molecular length much lower, being only about 40-41 Å, which
perfectly fitted to the experimental values.
For homologue TLL10/* with a methylbutyl fragment and two
lactates in the chiral chain, we proved the presence of the SmC*-
SmCA* phase sequence. We measured polarisation, Ps, and tilt
angle, Hs; within both mesophases and confirmed that TLL10/*
revealed the best orthoconic properties. We proved the ferro-
antiferroelectric sequence by dielectric spectroscopy. A strong
Goldstone mode was observed in the SmC* phase and a large
decrease in permittivity in the SmCA* phase. Generally, two relax-
ation processes can be observed by dielectric spectroscopy in the
SmCA* phase. For the compound TLL10/*, we detected only one
weak mode, which we tentatively ascribed to the anti-phase col-
lective mode. As all modes in any antiferroelectric phase are
expected to be very weak, other collective or molecular dynamics
can be supressed by additional processes or effects like conductiv-
ity, high viscosity, etc. In any case, the antiferroelectric character
for TLL10/* was fully confirmed by several experimental methods.
We can conclude that in these terphenyl derivatives we opti-
mised their mesomorphic properties and reached the orthoconic
antiferroelectric phase persisting at room temperatures. Due to
their orthoconic properties, all studied compounds are promising
for mixtures, which can be tuned for display and also non-
display applications.
[9] R. Dabrowski, W. Drzewinski, J. Dziaduszek, J. Gasowska, P.A. Henderson, P.
Kula, J.M. Oton, N. Bennis, Orthoconic antiferroelectric liquid crystals
containing biphenyl, terphenyl, or naphthyl mesogenic unit, Opto-Electro.
Rev. 15 (2007) 32–36.
[10] L. Szczucinski, R. Dabrowski, S. Urban, K. Garbat, M. Filipowicz, J. Dziaduszek,
M. Czerwinski, Synthesis, mesogenic and dielectric properties of
fluorosubstituted isothiocyanatoterphenyls, Liq. Cryst. 42 (2015) 1706–1729.
[11] D. Pauluth, K. Tarumi, Advanced liquid crystals for television, J. Mater. Chem.
14 (8) (2004) 1219–1227.
[12] N. Chernova, M. Loseva, E. Pozhidaev, N. Korotkova, Synthesis and ferroelectric
properties of some chiral dopants with a terphenyl central core, Ferroelectrics
138 (1993) 95–101.
[13] M.E. Glendenning, J.W. Goodby, M. Hird, K.J. Toyne, The synthesis and
´
´
´
´
´ ´ ´
mesomorphic properties of 2,2,3- tri- and 2,2,3,3-tetra-fluoro-1,1:4,1-
terphenyls for high dielectric biaxiality ferroelectric liquid crystal mixtures,
J. Chem. Soc., Perkin Trans. 2 (1999) 481–491.
[14] A.A. Kiryanov, P. Sampson, A.J. Seed, Synthesis and mesomorphic properties of
1,1-difluoroalkyl-substituted biphenylthienyl and terphenyl liquid crystals. A
comparative study of mesomorphic behaviour relative to alkyl, alkoxy and
alkanoyl analogs, J. Mater. Chem. 16 (2006) 907–961.
[15] V.S. Bezborodov, V.M. Kondratenkov, V.I. Lapanik, D.A. Trokhimets, Synthesis
and mesomorphic properties of 4-alkyl-3,4’-disubstituted biphenyls and
terphenyls, Liq. Cryst. 10 (1991) 799–802.
[16] P. Kula, J. Herman, O. Chojnowska, Synthesis and properties of terphenyl- and
quaterphenyl-based chiral diesters, Liq. Cryst. 40 (2013) 83–90.
[17] A. Wachala, M. Pytlaczyk, P. Kula, On the balance between nematic and
smectic phases in 20,30-difluoro-4,400 -dialkyl-p-terphenyls, Liq. Cryst. 46
(2019) 1558–1567.
ˇ
[18] V. Novotná, V. Hamplová, M. Glogarová, L. Lejcek, E. Gorecka, Effect of the
applied electric field on new cholesterics with extremely short pitch, Liq.
Cryst. 45 (2018) 634–640.
ˇ
[19] V. Novotná, L. Fekete, V. Hamplová, M. Glogarová, L. Lejcek, M. Cigl, D.
Funding
Pociecha, Effect of lactate group in the chiral chain of new compounds
exhibiting short-pitch cholesteric or TGBA phase, Liq. Cryst. 45 (2018) 1155–
1163.
Authors acknowledge the Czech Ministry of Education, Youth
and Sports [project number LTC19051] and Operational Pro-
gramme Research, Development and Education financed by Euro-
[20] N. Podoliak, V. Novotná, M. Kašpar, V. Hamplová, M. Glogarová, D. Pociecha,
Anomalous phase sequence in new chiral liquid crystalline materials, Liq.
Cryst. 41 (2) (2014) 176–183.
8

ˇ
N. Podoliak, M. Cigl, Vera Hamplová et al.
Journal of Molecular Liquids 336 (2021) 116267
[21] V. Novotná, M. Kašpar, V. Hamplová, N. Podoliak, M. Glogarová, D. Pociecha,
Ferroelectric, antiferroelectric and TGB phases in lactic acid derivatives, Liq.
Cryst. 39 (2012) 477–486.
[28] M. Kašpar, V. Novotná, V. Hamplová, D. Pociecha, M. Glogarová, Phase diagram
of new lactic acid derivatives exhibiting ferro- and antiferroelectric phases,
Liq. Cryst. 35 (2008) 975–985.
[22] M. Kašpar, P. Bílková, A. Bubnov, V. Hamplová, V. Novotná, M. Glogarová, K.
[29] M. Kašpar, V. Novotná, V. Hamplová, N. Podoliak, D. Nonnenmacher, F.
Giesselmann, M. Glogarová, Antiferroelectric phase in liquid crystalline
compounds with azo group in their molecular core, Liq. Cryst. 38 (2011)
309–315.
[30] V. Novotná, M. Glogarová, V. Hamplová, M. Kašpar, Re-entrant ferroelectric
phases in binary mixtures of ferroelectric and antiferroelectric homologues of
a series with three chiral centers, J. Chem. Phys. 115 (15) (2001) 9036–9041.
[31] V. Hamplová, A. Bubnov, M. Kašpar, V. Novotná, D. Pociecha, M. Glogarová,
New ferroelectric and antiferroelectric liquid crystalline materials containing
different numbers of lactate units, Liq. Cryst. 30 (2003) 627–631.
[32] V. Hamplová, A. Bubnov, M. Kašpar, V. Novotná, Y. Lhotáková, M. Glogarová,
New antiferroelectric liquid crystalline materials with the keto group and two
lactate groups, Liq. Cryst. 30 (2003) 1463–1469.
ˇ
Knízek, D. Pociecha, New chlorine-substituted liquid crystals possessing
frustrated TGBA and SmQ phases, Liq. Cryst. 35 (5) (2008) 641–651.
[23] V. Novotná, S. Stulov, M. Cigl, V. Hamplová, E. Gorecka, D. Pociecha,
Mesomorphic properties of lactic acid derivatives and their racemic
mixtures in comparison with analogous non-chiral compounds, Liq. Cryst.
47 (2020) 1516–1527.
ˇ
[24] V. Novotná, V. Hamplová, L. Lejcek, D. Pociecha, M. Cigl, L. Fekete, M.
Glogarová, L. Bednárová, P. Majewski, E. Gorecka, Organic nanotubes created
from mesogenic derivatives, Nanoscale Adv. 1 (2019) 2835–2839.
[25] I. Nishiyama, J. Yamamoto, J.W. Goodby, H. Yokoyama, Novel non-symmetric
chiral twin liquid crystals possessing two identical chiral moieties at both
peripheral ends: highly chirality sensitive phases appeared between smectic
and isotropic liquid phases, J. Mater. Chem. 12 (2002) 1709–1716.
[26] I. Nishiyama, Y. Tabe, J. Yamamoto, H. Yokoyama, Pre-organization effects on
chirality, polarity and biaxiality in liquid crystals: novel laterally connected
mesogens showing anomalous properties, Mol. Cryst. Liq. Cryst. 549 (2011)
174–183.
ˇ
[33] M. Kašpar, V. Hamplová, V. Novotná, M. Glogarová, D. Pociecha, P. Vanek, New
series of ferroelectric liquid crystals with two or three chiral centres exhibiting
antiferroelectric and hexatic phases, Liq. Cryst. 28 (2001) 1203–1209.
[34] V. Novotná, V. Hamplová, G. Sasnouski, P. Salamon, Lactic acid derivatives with
terphenyl molecular core, Liq. Cryst. 43 (2016) 1251–1258.
[27] V. Novotná, M. Kašpar, V. Hamplová, M. Glogarová, I. Rychetsky´, D. Pociecha,
Direct phase transition from the SmA phase to the tilted hexatic phase in
liquid crystals with several lactate units, Liq. Cryst. 31 (2004) 1131–1141.
9