Dependence of mesomorphism on flexibility of lateral and terminal groups of chalconyl esters

Article abstract of DOI:10.1080/15421406.2016.1217702

A novel liquid crystalline homologous series of chalconyl vinyl esters with a lateral bromo substituent RO─C₆H₄─CH═CH─COO─C₆H₃─(Br)─CO-CH═CH─C₆H₄─C₁₂H_25(n) has been synthesized and studied with a view to understanding and establishing the relation between the molecular structure and liquid crystal (LC) behavior in terms of molecular flexibility of the lateral and terminal groups. The novel homologous series consists of thirteen (C₁–C₁₈) homologues, whose enantiotropic nematic and smectic mesomorphism commences from the C₄, (C₄–C₁₈) and the C₅, (C₅–C₁₈) homologue, respectively. The rest of the homologues (C₁, C₂, C₃) are nonliquid crystals (NLC). Mesomorphism and transition temperatures were examined using an optical polarising microscope (POM) equipped with a heating stage. Textures of nematic phase are threaded or Schlieren and those of the Smectic-A or Smectic-C are focal conic. Analytical, thermal and spectral data supported molecular structures of the novel homologues. Thermal for smectic and nematic are 87.5°C and 101.1°C, respectively, whose, total mesophase length ranges from 17°C to 30°C at C₁₄ and C₇ homologue, respectively. The mesomorphic transition temperature ranges are between 70°C and 113°C.

Full text of DOI:10.1080/15421406.2016.1217702

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Dependence of mesomorphism on flexibility of
lateral and terminal groups of chalconyl esters
Priya K. Patel & R. R. Shah
To cite this article: Priya K. Patel & R. R. Shah (2016) Dependence of mesomorphism on
flexibility of lateral and terminal groups of chalconyl esters, Molecular Crystals and Liquid
Crystals, 641:1, 1-9, DOI: 10.1080/15421406.2016.1217702
To link to this article: http://dx.doi.org/10.1080/15421406.2016.1217702
Published online: 15 Dec 2016.
Submit your article to this journal
Article views: 4
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
http://www.tandfonline.com/action/journalInformation?journalCode=gmcl20
Download by: [FU Berlin]
Date: 20 December 2016, At: 23:58

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
http://dx.doi.org/./..
Dependence of mesomorphism on flexibility of lateral and
terminal groups of chalconyl esters
Priya K. Patel and R. R. Shah
Chemistry Department, K. K. Shah Jarodwala Maninagar Science College, Gujarat University, Ahmedabad,
Gujarat, India
ABSTRACT
KEYWORDS
Azoester; chalconyl ester;
liquid crystals; nematic;
smectic
A novel liquid crystalline homologous series of chalconyl vinyl
esters with a lateral bromo substituent RO─C6H4─CH═CH─COO─C6
H3─(Br)─CO-CH═CH─C6H4─C12H25(n) has been synthesized and studied
with a view to understanding and establishing the relation between
the molecular structure and liquid crystal (LC) behavior in terms of
molecular flexibility of the lateral and terminal groups. The novel
homologous series consists of thirteen (C1–C18) homologues, whose
enantiotropic nematic and smectic mesomorphism commences from
the C4, (C4–C18) and the C5, (C5–C18) homologue, respectively. The rest of
the homologues (C1, C2, C3) are nonliquid crystals (NLC). Mesomorphism
and transition temperatures were examined using an optical polarising
microscope (POM) equipped with a heating stage. Textures of nematic
phase are threaded or Schlieren and those of the Smectic-A or Smectic-
C are focal conic. Analytical, thermal and spectral data supported
molecular structures of the novel homologues. Thermal for smectic and
nematic are 87.5°C and 101.1°C, respectively, whose, total mesophase
length ranges from 17°C to 30°C at C14 and C7 homologue, respectively.
The mesomorphic transition temperature ranges are between 70°C and
113°C.
Introduction
The potential dual utility of LC chalconyl ester derivatives [1] to operate LC devices at room
temperature and exploitation of their bioactivity as antifungal, antibacterial, antimalarial,
antioxidant, anticancer etc. is beneficial through pharmaceutical or agricultural industrial
production [2–9] and inspired the present investigation; with a view to understanding and
establishing the effects of molecular structure on thermotropic LC properties [10–15]. The
object in view is to synthesize novel chalconyl ester derivatives through homologous series,
characterization of novel materials through analytical, thermal and spectral methods. The
results are discussed and interpreted in terms of molecular rigidity and flexibility [16–19] and
finally conclusions are drawn qualitatively including probable utility. Group efficiency order
will be derived on the basis of thermal stabilities, early commencement of mesophase and
mesophase length from comparative study of present novel series with structurally similar
analogous series derived from cis-trans isomeric cinnamic acids. Several homologous series
of esters, azoesters, chalconyl esters, benzyl esters have been reported to date [20–25].
CONTACT R. R. Shah
ruteshshah@gmail.com
lege, Ahmedabad-, Gujarat University, Ahmedabad, Gujarat, India.
Chemistry Department, K. K. Shah Jarodwala Maninagar Science Col-
©  Taylor & Francis Group, LLC

2
P. K. PATEL AND R. R. SHAH
Experimental
Synthesis
4-Hydroxy benzaldehyde was alkylated by using suitable alkyl halides (R-X) to generate
4-n alkoxy benzaldehyde (A) which reacts with malonic acid, in presence of piperidine and
pyridine to form trans 4-n alkoxy cinnamic acid (B).
α-3-Bromo-4-hydroxy benzoyl-β-4ꢀ-n-dodecyloxy phenyl ethylene (C) was prepared by
a usual established method [26]. 4-n-Alkoxy cinnamic acids and α-3-bromo-4-hydroxy
benzoyl-β-4ꢀ-dodecyloxy phenyl ethylene were condensed in 1, 3-dicyclohexyl carbodiimide
(DCC), 4-dimethyl amino pyridine (DMAP) and CH2Cl2 (DCM) [27] to obtain α-4-(4ꢀ-n-
alkoxy Cinnamoyloxy) 3-bromo benzoyl β-4ꢀ-dodecyloxy phenyl ethylenes (D) [28]. Final
products were filtered, washed, dried and purified until constant transition temperatures
obtained. The synthetic route to the novel homologous series of ethylene derivatives is shown
in Scheme 1.
Characterization
Some selected representative homologues of the series were characterized by infrared
[IR],1HNMR technique and elemental analysis. IR spectra were recorded on Perkin Elmer
spectrum GX.1HNMR spectra were recorded on a Bruker spectrometer using CDCl3 as sol-
vent. Elemental analysis was performed on Perkin Elmer PE 2400 CHN analyzer (Table 1).
Table 1 shows elemental analysis of mesomorphs and Table 2 shows textures of different
phases. Liquid Crystal properties i.e. transition and melting temperatures of homologues were
investigated by an optical polarizing microscopy equipped with heating stage. Textures of the
novel homologues were determined by miscibility method.
Analytical data
IR Spectra in cm− for Hexyloxy and Hexadecyloxy Derivatives
Hexyloxy. 501.49 and 651.94 (─CH-Br str.), 721.38 and 767.67 (polymethylene (─CH2)n of
─OC6H13), 833.25 (─C─H def. of m, p-disubstituted), 979.84 (─C─H def. of hydrocarbon),
1033.85, 1053.13, 1111.00, and 1172.72 (─C─O str.), 1249.87, 1307.74, 1423.47, and 1469.76
(─C─O str. in (-CH2)n chain), 1512.19 (─C─H def. in ─CH), 1573.91 (─C═C- str.), 1600.92
(─C═O group), 1689.64 (─COO─ ester group), 2850.79, and 2920.23 (─C─H str. in ─CH3).
IR confirms the structure.
Hexadecyloxy. 520.78 and 651.94 (─CH─Br str.), 721.38 and 763.81 (polymethylene
(─CH2)n of ─OC16H33), 833.25 (─C─H def. of m, p-disubstituted), 979.84 (─C─H def.
of hydrocarbon), 1033.85, 1053.13, 1111.00, and 1161.15 (─C─O str.), 1249.87, 1307.74,
1427.32, and 1465.90 (─C─O str. in (─CH2)n chain), 1512.19 (─C─H def. in ─CH2), 1573.91
(─C═C─ str.), 1600.92 (─C═O group), 1689.64 (─COO─ ester group), 2850.79 and 2920.23
(─C─H str. in ─CH3), IR confirms the structure.
 HNMR spectra in CDCl in δ ppm for Heptyloxy and Octadecyloxy Derivative
Heptyloxy. 0.78 and 1.00 (─CH3 of ─OC7H15), 2.74 & 3.27 (─CH═CH─), 3.76 (t,
─OCH2─CH2─ of ─OC7H15), 5.02 (─OCH2 of ─OC7H15), 6.06 (p-substituted phenyl ring).
NMR confirms the structure.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
3
Scheme . Synthetic route to the series.
Octadecyloxy. 0.89 (─CH3 of ─OC18H37), 1.26 (─(CH2)n -polymethylene group of
─OC18H37), 3.82 (t, ─OCH2─CH2─ of ─OC18H37), 4.98 (─OCH2 of ─OC18H37), 8.1 (p-
substituted phenyl ring), 3.03 (─CH═CH─). NMR confirms the structure.
Results and Discussion
α-3-Bromo-4-hydroxy benzoyl-β-4ꢀ-n-dodecyloxy phenyl ethylene (m.p.: 87°C) was con-
densed with trans 4-n-Alkoxy cinnamic acids to yield novel chalconyl ester derivatives C1

4
P. K. PATEL AND R. R. SHAH
Table . Elemental analysis for butyloxy, pentyloxy, octyloxy, decyloxy.
Element % found
Element % calculated
H
Molecular formula
C
H
Br
C
Br
CHOBr
CHOBr
HOBr
.%
.%
.%
.%
.%
.%
.%%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
C
CHOBr
Table . Textures of nematic phase of C, C, C, and C by miscibility method.
Sr. No.
Homologue
Texture

C
C
C
C
Threaded nematic
Smectic A



Smectic A
Smectic C
Homologous series: α- [ꢀ-n-alkoxy cinnamoyloxy] -bromo benzoyl β-ꢀ dodecyloxy phenyl ethylenes.
to C18 homologues. The C1 to C3 homologues are nonliquid crystals but the rest of the homo-
logues C4 to C18 are enantiotropically liquid crystals. All the mesomorphic homologues are
smectogenic plus nematogenic except C4 homologue, which exhibited only nematic prop-
erty without exhibition of smectic property. Transition temperatures of novel homologues are
lower than corresponding n-alkoxy cinnamic acids. Alternation of transition temperatures
are observed from C4 to C8. Transition and melting temperatures (Table 3) as determined
from POM equipped with a heating stage were plotted against the number of carbon atoms
present in n-alkyl chain ‘R’ of –OR group and then, transition curves Cr-M/I, Sm-N and N-I
are obtained on linking like or related points, as shown in Fig. 1 of a phase diagram. Sm-N
Table . Transition temperature in°C.
Transition temperatures in°C
Compound no.
Homologue (n-alkyl chain)
Smectic
Nematic
Isotropic













C
C
C
C
C
C
C
C
C
C
C
C
C
—
—
—
—
—
—
.
.
.
.
.
.
.
.
.
.
—
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
Homologous series: α- [ꢀ-n-alkoxy cinnamoyloxy] -bromo benzoyl β-ꢀ dodecyloxy phenyl ethylenes.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
5
Figure . Phase behavior of series.
and N-I transition curves exhibited odd-even effect up to C8 and C9 homologues, respectively,
beyond which odd-even effects disappears for higher homologues of longer n-alkyl chain ‘R’
of ─OR group. The LC property commenced from C4 homologue and it varies from homo-
logue to homologue in the same novel series. Thermal stabilities for smectic and nematic are
87.5 and 101.1, respectively, whose Sm-N mesophase lengths vary from 7.0°C to 15.0°C and
N-I mesophase length vary between 8.0°C and 29.0°C. Analytical, thermal and spectral data
confirmed the molecular structures of homologues.
Condensation of vinyl carboxy acids with chalcone, increases the molecular length, perma-
nent dipole moment across the long molecular axis, suitable magnitudes of anisotropic forces
of intermolecular end to end and lateral attractions as a consequence of effective molecu-
lar rigidity and flexibility, which facilitate mesophase formation from C4 member of a novel
series. The lowering of transition temperatures of novel homologues as compared to the cor-
responding n-alkoxy trans cinnamic acid is attributed to the breaking of hydrogen bond-
ing between their two molecules by esterification process. The combined effect of molecular
structural rigidity and flexibility operating the suitable magnitudes of anisotropic forces of
end to end and lateral intermolecular attractions and favorable closeness do not induce either
nematic or smectic mesophase from C1 to C3 homologues due to their high crystallizing ten-
dency as a result of respective low magnitudes of dispersion forces and the low magnitudes of
dipole–dipole interactions. However, favorable and suitable magnitudes of anisotropic forces
of intermolecular end to end and lateral attractions due to the effective polarizability con-
tributed by ─Br polar flexible lateral group and two terminally situated flexible polar end
groups, initiated from C4 and ended to C18 homologue, which, disalign the molecules at
an angle ninety degree or/and less than ninety degree with the plane of floating surface; to

6
P. K. PATEL AND R. R. SHAH
Figure . Structurally similar analogous series.
arrange the molecules in sliding layered molecular organization and/or then in statically par-
allel orientational ordered organization under the influence of exposed thermal vibrations
for different range of temperature from homologue to homologue in the same series. Thus,
smectic plus nematic (C5–C18) or only nematic mesophase (C4) facilitated. None of the non-
mesogenic homologues (C1, C2, C3) did show monotropic mesophase formation on cooling
below isotropic temperature in irreversible manner due to their high crystallising tendancy.
The appearance of odd-even effect in the Sm-N or N-I transition curves of a phase diagram
up to C8 or C9 homologue is attributed to the gradual and sequential addition of a methy-
lene unit for the shorter n-alkyl. The odd-even effect disappears from and beyond higher
homologues of longer than C8 or C9. The low thermal stabilities for smectic and nematic in a
series containing ─CH═CH─ units in the both central bridges is attributed to the presence of
laterally substituted polar and polarizable Bromo flexible group which broadens a molecule
and increases intermolecular distance. The variations in mesomorphic properties from homo-
logue to homologue in the present novel series is attributed to the changing number of carbon
atoms present in n-alkyl chain ‘R’ of ─OR group, keeping the rest of the molecular part unal-
tered; which causes variation in molecular flexibility, keeping molecular rigidity unchanged.
The mesomorphic properties or behaviors of present novel series-1, are compared with the
structurally similar analogous series-X [29] and Y [30] as in Fig. 2.
Figure 2 represents that, present novel homologous series-1, X and Y are identi-
cal with respect to three phenyl rings and two central bridges ─CH═CH─COO─ and
─CO─CH═CH─ which constitutes total molecular rigidity depending upon shape, size and
induced flexibility of terminal and lateral groups as well as their polarity and polarizability.
The left n-alkoxy group –OR and tailed ended ─OC12H25(n) of series-1 and X are same for
the same homologue from series to series, but their geometrical shapes as well as presence
of lateral group ─Br and ─H are different; whose polarity and polarizabilities or the ratio of
the molecular polarity and polarizability causes differences in the magnitudes of molecular
flexibility. Homologous series-1 and Y are identical with respect to geometrical shapes, for
the same homologue from series to series, but, they differ with respect to tailed ended groups
─OC12H25(n) and ─OC14H29(n) including effect due to cis-trans isomerism of vinyl carboxylic
acids as well as polarizability or the ratio of the polarity to polarizability affecting magnitudes
of molecular flexibility for the same homologue from series to series. Thus, variations in LC
properties, behaviors and the degree of mesomorphism are depended upon the magnitudes of
differing features amongst the series-1, X and Y for the same homologue from series to series
or from homologue to homologue in the same series, affecting the combined effect of molecu-
lar rigidity plus flexibility which operates, the suitable or unsuitable magnitudes of anisotropic

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
7
Table . Relative thermal stabilities in°C.
Series→
Series-
Series-X
Series-Y
Sm-N or Sm-I
Commencement of smectic phase
N-I
.
.
(C–C) C
.
(C–C) C
—
.
.
Commencement of nematic phase
(C–C) C
(C–C) C
(C–C) C
Total mesophase length (Sm + N) in°C from minimum to maximum . to . C C . to . C C . to . C C
forces of intermolecular cohesion and closeness to facilitate or to not facilitate a phenomena
of mesomorphism. Following Table 4 represents some thermometrically evaluated data of the
analogous series-1, X and Y under comparative study.
Above Table 4 indicates that,
r
Homologous series-1 and X are smectogenic plus nematogenic but, series Y is only
nematogenic without exhibition of smectogenic property.
Smectogenic property commences from C5 homologue for present series-1 and a series-
X chosen for comparative study but, it does not commence till the last C18 homologue
of a series-Y.
The nematogenic mesophase commences from C4 homologue for series-1 and X, but it
commences late from C6 homologue of a series-Y.
Smectic thermal stability increases from series-1 to X but it does not stabilise at all for
series-Y.
r
r
r
r
The nematogenic thermal stabilities of series-1 and Y are lower than a series-X, i.e.,
Series-X > Series-Y > Series-1.
Total lower and upper mesophase lengths follow increasing order as under:
r
Lower: series-Y > series-1 > series-X
Upper: series-X > series-Y > series-1
Homologous series-1 and X derived from condensation of trans n-alkoxy cinnamic acids
and corresponding Bromo substituted 4-hydroxy or 3-hydroxy derivatives of 4ꢀ-dodecyloxy
chalcones. Therefore, Bromo substituted lateral group of series-1 and nonlinear shape of
series-X increases intermolecular attractions and distance due to enhancing polarizability.
But the enhancement in molecular polarizability in competition with intermolecular distance
which causes opposing effects i.e. reduction in intermolecular adhesive forces which predom-
inates in case of series-X as compared to series-1. Hence the lateral Bromo group of series-1
is less effective as compared to effectivity induced by polarizability factor through nonlinear
shape of a series-X. Thus, both series-1 and X commences smectic and nematic mesophases
from C5 and C4 homologues, respectively, in equal manner, but, the resulted magnitudes of
intermolecular attractions differs due to differing magnitudes of induced polarizability as a
consequence of combined effect of molecular rigidity and flexibility of series-1 and X, respec-
tively. Thus, resistivity toward exposed thermal vibrations and the internal energy stored
(ꢀH) by molecules for the same homologue from series to series and from homologue to
homologue in the same series differs, irrespective of identical commencement of smectic and
nematic phase; because the commencement of mesophase depends upon only suitable mag-
nitudes (not more or less) of anisotropic forces of intermolecular end to end or / and lateral
attractions. Homologous series-Y is synthesized from cis isomer of 4-n-alkoxy cinnamic acid
and 4-hydroxy derivative of 4ꢀ-tetradecyloxy chalcone. Therefore, carbonyl unit of chalcone
central bridge, though linked directly with middle phenyl ring like molecules of series-1 and
X, but, a lamellar packing of molecules in the crystal lattices of series-Y are not facilitated due
to cis configuration of cinnamic acid, whereas, it facilitated in case of molecules of series-1

8
P. K. PATEL AND R. R. SHAH
and X which are formed from trans configurated cinnamic acid. Thus, smectogenic character
is absent in the molecules of series-Y or only nematic property is exhibited by the molecules
of series-Y and smectic plus nematic property are exhibited by the molecules of series-1 and
X. Hence, cis-trans isomerism of a molecule can affect the extent of molecular noncoplanarity,
resistivity against exposed thermal vibrations, the degree of mesomorphism, type and extent
of disalignment of molecules on floating surface, thermal stability for smectic and nematic
and respective transition temperature as well as texture, magnitudes of energy stored (ꢀH),
magnitudes of dispersion forces, dipolarity of bond between carbon of phenyl ring and tailed
end group and dipole–dipole interactions, etc. Thus, presently investigated series-1 is pre-
dominantly nematogenic and partly smectogenic.
Conclusions
r
Novel chalconyl series with Bromo substituted lateral group ester series of liquid crystal is
predominantly nematogenic and partly smectogenic is of lower middle ordered melting
type series.
r
Trans configurated cinnamic acid derivatives of LC chalcone which links middle and
third phenyl ring by ─CO─CH═CH─ group facilitate the formation of smectic phase,
but, isomeric cis configurated cinnamic acid under identical condition, is missing facil-
itation of smectogenic mesophase formation.
r
Group efficiency order derived on the basis of (i) thermal stability, (ii) early commence-
ment of mesophase, and (iii) mesophase lengths for smectic and nematic are as under.
1. Smectic Nonlinear > Linear series-1 > Linear series-X with –Br lateral series-Y
group Nematic Series-X > Series-1 > Series-Y
2. Smectic Series-1 = Series-X > Series-Y Nematic Series-1 = Series-X > Series-Y
3. Total mesophaselength (Sm N)
Lower: Series-Y > Series-1 > Series-X
Upper: Series-X > Series-Y > Series-1
r
Cis-trans isomerism of a molecular structure affects a phenomena of mesomorphism,
the degree of mesomorphism and the type of texture of mesophase.
Mesomorphism is very sensitive and susceptible to a molecular structure as a conse-
quence of effective molecular rigidity and flexibility.
Study of biological activity and application of thermotropic LC at desired temperature
can be useful to the mankind.
Present novel investigation supports and raises the conclusions drawn earlier and con-
tribute more to the existing conclusions.
r
r
r
Acknowledgments
The authors thank the management of the college and the Head of the Chemistry Department, Dr. R.
B. Patel of K. K. Shah Jarodwala Maninagar Science College, Ahmedabad for their valuable coopera-
tion in the work. The authors are also thankful to Dr. A. V. Doshi, Ex-Principal, M. V. M. Science and
Homescience College, Rajkot for his co-operation, valuable suggestions, comments, and help as and
when needed during the course of present investigation. Thanks are due to NFDD Centre, Saurashtra
University, Rajkot for analytical and spectral services.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
9
References
[1] Reinitzer, F. (1888). Monatsh, 9, 421.
[2] Narmura, S. (2001). Displays, 22(1), 1.
[3] Kim, W. S., Elston, S.J., & Raynes, F.P. (2008). Displays, 29, 458–463.
[4] Imaran, T., Sahanashahi, V.R., & Iftequar, S. (2012). IJPRAS, 1(2), 06–11.
[5] Calliste, C.A. et al. (2001). Anticancer, Res., 21, 3949–3956.
[6] Rajesh, G. et al. (2008). Chem. Pharm. Bull., 56, 897–901.
[7] Gaikwad, P.P., & Desai, M.T. (2013). Int. J. Pharma Res. Rev., 2 (12), 40–52.
[8] Benjamin, B. et al. (2007). Patent No.: WO2007140510A1.
[9] Rohini, M. et al. (2013). Int. J. Pharm. Sci. Rev. Res., 22 (2), 109–115.
[10] Imrie, C.T. (1999). Struct. Bond, 95, 149–192.
[11] Gray, G.W. (1974). In: Liquid Crystals and Plastic Crystals, Gray, G.W. & Winsor, P.A. (Eds.),
Chapter 4, Volume 1, Ellis Horwood, Chichester, U.K., 103–153.
[12] Gray, G.W. (1962). Molecular Structures and Properties of Liquid Crystals, Academic Press:
London.
[13] Gray, G.W., & Winsor, P.A. (Eds.) (1974). In: Liquid Crystals and Plastic Crystals, Chapter 6.2: The
role of liquid crystal in life processes by Stewart, G.T., Volume 1, Taylor & Francis, U.K., 308–326.
[14] Henderson, P.A., Niemeyer, O., & Imrie, C.T. (2001). Liq. Cryst., 28, 463–472.
[15] Imrie, C.T., & Luckhrust, G.R. (1998). In: Liquid Dimers and Oligomers in Handbook of Liquid
Crystal, Law Molecular Liquid Crystals; Vol. 2B, Demus, D., Goodby, J.W., Gray, G.W., Spiess, H.
& Vill, V. (Eds.), Wiley-VCH: Weinheim, 801–833.
[16] Hird, M., Toyne, K.J., Gray, G.W., Day, S.E., & McDonell, D.G. (1993). Liq. Cryst., 15, 123.
[17] Collings P.J., & Hird, M. (1997). Introduction of Liquid Crystals Chemistry and Physics, Taylor and
Francis Ltd: U.K.
[18] Marcos, M., Omenat, A., Serrano, J.L., & Ezcurra, A. (1992). Adv. Matter, 4, 285.
[19] Hird, M., Toyne, K.J., Gray, G.W., & Day, S.E. (1993). Liq. Cryst., 14, 741.
[20] Demus, D. (1988). Mol. Cryst. Liq. Cryst., 165, 45–84.
[21] Demus, D. (1988). Liq. Cryst., 5, 75–110.
[22] (i) Suthar, D.M., & Doshi, A.V. Mol. Cryst. Liq. Cryst., 575, 76–83. (ii) Chauhan, H.N. & Doshi,
A.V. (2013). Mol. Cryst. Liq. Cryst., 570, 92–100. (iii) Chaudhary, R.P., Chauhan, M.L., & Doshi,
A.V. (2013). 575, 88–95. (iv) Bhoya, U.C., Vyas, N.N., & Doshi, A.V. (2012). Mol. Cryst. Liq. Cryst.,
552, 104–110.
[23] Suthar, D.M., Doshi, A.A., & A.V. (2013). Mol. Cryst. Liq. Cryst., 582, 79–87.
[24] Patel, B.H., Patel, V.R., & Doshi, A.V. (2015). Mol. Cryst. Liq. Cryst., 609, 10–18.
[25] Marathe, R.B., & Doshi, A.V. (2015). Mol. Cryst. Liq. Cryst., 623, 1–8.
[26] Dave, J.S., & Vora, R.A. (1970). In: Liquid Crystals and Ordered Fluids, Johnson J.F. & Porter R.S.,
(Eds.), Plenum Press: New York, 477.
[27] Vogel, A.I. (1989). Textbook of Practical Organic Chemistry. 5th ed., ELBS and Longmann: London,
946.
[28] Uhood, J.A. (2011). Int. J. Mol. Sci., 12, 3182–3190.
[29] Patel, P.K., & Shah, R. R. (2016). Mol. Cryst. Liq. Cryst., 637, 37–46.
[30] Jain, B.B., & Patel, R.B. (2015). ILCPA, Scipress, 58, 16–25.