The effect of geometrical shape and molecular rigidity on mesomorphism

Article abstract of DOI:10.1080/15421406.2016.1190509

A novel nonlinear homologous series RO?C₆H₄?CH?CH?COO?C₆H₄ (meta) ?CO?CH?CH?C₆H₄?OC₁₂H_25(n) (para) consisting of three phenyl rings, two central bridges ?CH?CH?COO? and ?CO?CH?CH? as well as ?OR and ?OC₁₂H_25(n) as flexible and constant terminal end groups respectively. The object in view is aimed to understand and establish the effect of molecular structure on LC properties of nonlinear inverted “V” shaped molecules. Novel homologous series consists of thirteen homologues. Transition temperatures and textures were determined by polarizing optical microscopy (POM) equipped with a heating stage. Textures of nematic phases are threaded or schlieren and that of a smectic phases are of the type-A or C. Transition curves of a phase diagram behaved in a normal manner. Sm-N and N-I transition curves exhibited odd-even effect. Analytical, Thermal and Spectral data confirms the molecular structure of homologues.

Full text of DOI:10.1080/15421406.2016.1190509

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
The effect of geometrical shape and molecular
rigidity on mesomorphism
Priya K. Patel & R. R. Shah
To cite this article: Priya K. Patel & R. R. Shah (2016) The effect of geometrical shape and
molecular rigidity on mesomorphism, Molecular Crystals and Liquid Crystals, 637:1, 37-46, DOI:
10.1080/15421406.2016.1190509
To link to this article: http://dx.doi.org/10.1080/15421406.2016.1190509
Published online: 10 Nov 2016.
Submit your article to this journal
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: [University of Waterloo]
Date: 11 November 2016, At: 00:20

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –

http://dx.doi.org/./..
The effect of geometrical shape and molecular rigidity
on mesomorphism
Priya K. Patel and R. R. Shah
Chemistry Department, K. K. Shah Jarodwala Maninagar Science College, Gujarat University, Ahmedabad,
Gujarat, India
ABSTRACT
KEYWORDS
A novel nonlinear homologous series RO–C H –CH=CH–COO–C H
Chalconyl LC; liquid crystals;
mesogens; nematic; smectic
6
4
6
4
(
meta) –CO–CH=CH–C H –OC H
(para) consisting of three phenyl
6
4
12 25(n)
rings, two central bridges –CH=CH–COO– and –CO–CH=CH– as well as
–
ORand –OC H
as flexible andconstantterminalendgroups respec-
1
2
25(n)
tively. The object in view is aimed to understand and establish the effect
of molecular structure on LC properties of nonlinear inverted “V”shaped
molecules. Novel homologous series consists of thirteen homologues.
Transition temperatures and textures were determined by polarizing
optical microscopy (POM) equipped with a heating stage. Textures of
nematic phases are threaded or schlieren and that of a smectic phases
are of the type-A or C. Transition curves of a phase diagram behaved in
a normal manner. Sm-N and N-I transition curves exhibited odd-even
effect. Analytical, Thermal and Spectral data confirms the molecular
structure of homologues.
Introduction
Mesomorphic behaviors of a liquid crystalline (LC) substance [1] of either thermotropic or
lyotropic type are dependent on the number of variable factors like aromaticity through the
number of phenyl rings involved, polarities of terminal and/or central bridge or bridges, shape
and size, ratios of length to breadth and the molecular polarity and polarizability, magni-
tudes of dipole–dipole interactions and intermolecular dispersion forces, substitution of func-
tional group or groups on same or different phenyl ring or rings of isomeric or nonisomeric
molecules, etc., or in general molecular rigidity and/or flexibility [2,3,4,5] of the differing
molecular structure [6,7,8,9,10,11,12]. Present investigation is planed with a view to under-
stand the relation between molecular structure and mesomorphism with reference to the geo-
metrical shape of a molecule and the functional groups involved at central bridge liking phenyl
rings and terminally situated end groups. Proposed novel substances will contain three phenyl
rings, two central bridges, and two terminal group with inverted “V” shape of molecules. Study
will involve synthesis, characterization of novel substances through elemental analysis, spec-
tral data, and thermometric data obtained through an optical polarizing microscopy (POM)
equipped with a heating stage. Evaluated thermal data will be discussed and interpreted
in terms of molecular rigidity and flexibility. Group efficiency order will be derived from
CONTACT R. R. Shah
lege, Gujarat University, Ahmedabad , Gujarat, India.
 Taylor & Francis Group, LLC
ruteshshah@gmail.com
Chemistry Department, K. K. Shah Jarodwala Maninagar Science Col-
©

3
8
P. K. PATEL AND R. R. SHAH
comparative study of structurally similar analogous series. Numbers of homologous series
with thermotropic LC ester linkages have been reported to date [13,14,15,16,17,18].
Experimental
Synthesis
4
4
-Hydroxy benzaldehyde was alkylated by using suitable alkyl halides (R-X) to convert it into
-n alkoxy benzaldehyde (A), which reacts with malonic acid, in presence of piperidine and
pyridine to form 4-n alkoxy cinnamic acid (B) [19].
ꢀ
α-3-Hydroxyl benzoyl β-4 -dodecyloxy phenyl ethylene (C) was prepared by usual estab-
lished method [20]. Chalconyl esters were synthesized by condensing (B) and (C) using lit-
erature method [21]. Thus, the Chalconyl–ester homolog derivatives were filtered, washed
with sodium bicarbonate solution followed by distilled water, dried, and purified till con-
stant transition temperatures obtained using an optical polarizing microscope equipped with
a heating stage (POM). Alkyl halides, 4- hydroxy benzaldehyde, 4-hydroxy acetophenone,
dicyclohexyl carbodimide, dimethyl amino pyridine, DCM, MeOH, acetone, malonic acid,
pyridine, piperidine, etc., required for synthesis were used as received except solvents that
were dried and distilled prior to use. The synthetic route to a series is shown in Scheme 1.
Characterization
1
Some selected representative homologs of the series were characterized by infrared [IR], H
NMR technique, and elemental analysis. IR spectra were recorded on a Perkin Elmer spec-
1
trum GX. H NMR spectra were recorded on a Bruker using CDCl as solvent. Elemental anal-
3
ysis was performed on Perkin Elmer PE 2400 CHN analyzer (Table 1). Liquid crystal prop-
erties, i.e., transition and melting temperatures of homologs were investigated by an optical
polarizing microscopy with heating stage. Textures of the novel homologs were determined
by miscibility method.
Analytical data
Table . Elemental analysis for butyloxy, hexyloxy, decyloxy, and dodecyloxy.
Element % found
Element % calculated
Molecular formula
C
H
C
H
CH O
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%

C H O
  

CH O

CHO
−1
IR Spectra in cm for pentyloxy and tetradecyloxy derivatives:
Pentyloxy: 640.37, 734.88, 823.60 (polymethylene of (–CH ) of –OC H ), 937.40, 974.05
2
n
5
11
(
–CH=CH–), 1336.67, 1251.80, 1168.86 (–C–O stretching in (–CH ) chain), 1510.26 (C=C
2
stretching), 1602.85 (–C=O group, –COO ester group), 2848.86 (–CH stretching in –CH ),
3
3
032.10 confirms the =C–H of aromatic. The IR data are consistent with the molecular
structure.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
39
Scheme . Synthetic route to the series.
Tetradecyloxy: 638.44, 734.88, 831.32 (polymethylene (–CH ) of –OC H ), 937.40
2
n
14 29
(
1
(
–CH=CH–), 981.77 (–CH def. in hydrocarbon), 1099.43 (–C=O stretching), 1390.68,
253.73, 1168.86 (–C–O stretching in (–CH2) chain), 1510.26(–C=C– stretching), 1600.92
–C=O group, –COO ester group), 2850.79, 2920.23 (–CH stretching in –CH ), 3502.73 con-
3
firms the =C–H of aromatic. The IR data are consistent with the molecular structure.

4
0
P. K. PATEL AND R. R. SHAH
1
H NMR spectra in CDCl in δ ppm for heptyloxy and octadecyloxy derivatives:
3
Heptyloxy: 0.72–0.53 (t, –CH of –OC H ), 1.8–1.1 (m, n-polymethylene group of
OC H ), 2.7–2.0 (m, n-polymethylene group of –OC H ), 3.4–3.0 (s, –O–CH –CH of
3
7
15
–
7 15 7 15 2 2
–
OC H ), 5.4–5.1 (–O–CH –CH of –OC H ), 6.9–6.02 (s, –O–CH=CH), 11.3 (s, p-
7
15
2
2
7
15
disubstituted phenyl ring). The NMR data are consistent with the molecular structure.
Octadecyloxy: 0.42–0.99 (t, –CH of –OC H ), 1.40–1.00 (m, n-polymethylene group of
18 37 18 37 2 2
3
18 37
–OC H ), 2.48–1.59 (m, n-polymethylene group of –OC H ), 3.13 (s, –O–CH –CH of –
C H ), 7.76 (s, –O–CH=CH–). The NMR data are consistent with the molecular structure.
18
37
Table . Textures of nematic phase of C , C , C , C by miscibility method.


 
Sr. no.
Homolog
Texture

C
C
C
C
Threaded nematic
Threaded nematic
Smectic-A



Smectic-C
ꢀ
ꢀꢀ
Homologous series: α-3 [4 -n-alkoxy cinnamoyloxy] benzoyl β-4 -dodecyloxy phenyl
ethylenes.
Table . Transition temperature in °C.
Transition temperatures in °C
Compound no.
Homolog (n-alkyl chain)
Smectic
Nematic
Isotropic

C
C
C
C
C
C
C
C
C
C
C
C
C
—
—
—
—
—
—
.
.
.
.
.
.
.
.
.
.
.
.
.












—
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.




ꢀ
ꢀꢀ
Homologous series: α-3 [4 -n-alkoxy cinnamoyloxy] benzoyl β-4 -dodecyloxy phenyl
ethylenes.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
41
Figure . Phase behavior of series.
Results and discussion
Novel LC materials with 62.0°C to 164.0°C transition temperature range are synthesized by
condensation of trans 4-n-alkoxy cinnamic acids and nonmesogenic meta substituted chal-
ꢀ
conyl derivative containing hydroxy group (m.p.: 96°C, yield: 68%), which yielded α-3-(4 -n-
ꢀꢀ
alkoxy cinnamoyloxy) benzoyl β-4 -dodecyloxy phenyl ethylenes. Dimerization of n-alkoxy
cinnamic acids disappears on esterification and transition temperatures are lowered as com-
pared to corresponding n-alkoxy cinnamic acids. Nematogenic mesomorphism commences
from C homolog and continued up to last C homolog. Smectogenic mesophase commences
4
18
from C homolog and maintained up to C homolog prior to nematogenic mesophase for-
5
18
mation. Transition and melting temperatures (Table 3) as determined by POM equipped with
a heating stage, were plotted against the number of carbon atoms present in n-alkyl chain R
of –OR group. The transition curves, Cr-M/I, Sm-N, and N-I are obtained on linking like or
related transition points as depicted in a phase diagram (Fig. 1) showing their phase behaviors
of novel series. Cr-M/I transition curve follows zigzag path of rising and falling with overall
descending tendency and behaved in normal manner. Sm-N transition curve descends and
then passes through maxima at C homolog and descended up to C homolog with exhibi-
10
18
tion of very narrow and sharp odd-even effect. N-I transition curve continuously descended
from C to C homolog with exhibition of narrow and sharp odd-even effect. Thus, Sm-N and
4
18
N-I transition curves behaved in usual established expected normal manner. Curves involved
in odd-even effect for Sm-N and N-I are merging into each other at C homolog. N-I transi-
9
tion curves for odd members are occupying lower position, whereas, in Sm-N transition curve

4
2
P. K. PATEL AND R. R. SHAH
it (odd) occupies higher position as compared to even members. The odd-even effect dimin-
ishes as series is ascended from and beyond C homolog for longer n-alkyl chain “R” of higher
9
homologs of –OR and tailed ended –OC H
hydrocarbon chain bonded through oxygen
12
25(n)
atom with third phenyl ring. Mesomorphic properties from homolog to homolog in present
novel series undergoes variations. Molecular structures of homologs are confirmed by ana-
lytical, thermal, and spectral methods. The smectic and nematic thermal stabilities of present
novel series are 110.88 and 136.2, respectively. The total mesophase lengths are varied from
maximum to minimum, which is 54.0°C to 6.0°C at the C12 and C homolog, respectively.
4
Thus, present novel inverted “V”-shaped chalconyl ester series is predominantly nematogenic
and partly smectogenic. The extrapolation [22,23,24,25] of Sm-N and N-I transition curves
predicts latent transition temperatures (LTT) for smectic and nematic, as monotropic 132°C
and 161°C, respectively, of C and C homologs.
4
3
The lowering of transition temperatures of present novel homologs as compared to the cor-
responding trans n-alkoxy cinnamic acids is attributed to the breaking of hydrogen bonding
between two molecules of aromatic acid through esterification process. The absence of meso-
genic tendency of C and C homologs is attributed to low magnitudes of dispersion forces and
1
2
low magnitudes of dipole–dipole interactions, which, induces unsuitable magnitudes of inter-
molecular anisotropic forces of attractions and closeness as well as high crystallizing tendency
and inability to resist exposed thermal vibrations, which transforms the homologs C , C , and
1
2
C from crystalline solid state to direct isotropic state without passing through LC state and
3
vice versa on cooling the isotropic mass of the same, none of the mesomorphic homolog for
monotropic mesophase in irreversible manner due to their high crystallizing tendency. The
exhibition of nematic or/and smectogenic character is attributed to the suitable magnitudes
of anisotropic forces of intermolecular attractions and closeness as a consequence of favor-
able molecular rigidity and/or flexibility, which disalign the molecules of C to C homologs
4
18
at an angle less than 90 or/and at 90° with the plane of a floating surface. The molecules
that disaligned at an angle 90° (perpendicular to floating surface) possess lamellar packing
of molecules in their preoccupied crystal lattices, which forms layered structured molecu-
lar arrangement in solid crystals and high order of regularity and low entropy (ꢀS) toward
exposed thermal vibrations. Thus, on exposure of heat energy from exterior source, the inter-
molecular forces are loosened, but sliding layered molecular arrangement is maintained on
floating surface for a range or ranges of temperatures depending upon thermal resistivity of
sample homolog facilitating smectic mesophase formation (C to C ) but, the molecules that
5
18
disaligned at an angle less than 90° (C ) or facilitated smectic mesophase and possessed resid-
4
ual suitable magnitudes of anisotropic forces of intermolecular cohesion (C to C ), which
5
18
maintained the statistically parallel orientational order of molecules facilitated nematogenic
C to C ) mesophase formation for a range of temperature (only C ) and for another higher
(
4
18
4
range of temperature including smectic mesophase (C to C ). However, all the mesogenic
5
18
homologs (C to C ) on further heating exhibit isotropic state from and beyond isotropic
4
18
temperature at which molecules are randomly oriented in all possible directions with high
order of disorder or randomness or high entropy (ꢀS = ꢀH/T) in uncontrolled manner. How-
ever, on cooling the same from and below isotropic temperature, the mesogenic molecules
exhibited only nematic (C ) or nematic plus smectic mesophases reappearance (C to C )
4
5
18
exactly at a temperature and for temperature range at or during which it appeared on heating
in reversible manner. Such phase transitions are called enantiotropic transitions and temper-
atures are known as enantiotropic transition temperatures. The odd-even effect observed for
N-I and Sm-N transition curves is attributed to the odd and even numbered carbon atoms
present in n-alkyl chain “R” of –OR. The normal behaviors of transition curves of a phase

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
43
diagram indicates expected status of n-alkyl chain “R” of –OR and –OC H
terminal
25(n)
12
groups without any unexpected deviation. Occupation of higher or lower positions of odd
and even N-I or Sm-N transition curves depend upon molecular resistivity (ꢀH), as a result of
effective molecular rigidity and flexibility of odd or even homologs concerned. The variations
in mesomorphic properties of thermotropic LC substances from homolog to homolog in the
same series is attributed to the changing number of methylene (–CH -) unit or units whose
2
progressive and sequential addition increases molecular length, permanent dipole moment
across the long molecular axes, length to breadth ratio, intermolecular cohesions, molecular
polarity and polarizability, or the ratio of the polarity to polarizability, ratio of the molecu-
lar rigidity to flexibility, etc. The extrapolation of N-I and Sm-N transition curves, keeping
in view of the trend of respective curve to determine and predict LTT are 132°C (Smectic)
and 161°C (Nematic), which shows the latent ability of C and C homolog, and predicted
3
4
LTTs are hypothetical and not real or not realizable because, they are far below the isotropic
temperature and no sooner they exhibit predicted mesophase, they undergo crystallization
due to their high crystallizing tendency. Some thermometric properties of present inverted
“
V”-shaped novel chalconyl ester series-1 are compared with structurally similar analogous
nonisomeric series-X [26] and Y [27] as shown below in Fig. 2.
Figure . Structurally similar analogous series.
A novel homologous series-1 and X are nonisomeric to each other and identical with
respect to three phenyl rings, one (–CO–CH=CH) central bridge linking middle and third
phenyl rings, and left –OR end group as well as right –OC H
tailed end group for the
25(n)
12
same homolog from series to series. But they differ with respect to their geometrical shapes,
viz., nonlinear and linear, respectively, and central bridges –CH=CH–COO– and –COO-
linking first and middle phenyl rings, which causes variations in the magnitudes of molec-
ular rigidity and flexibility reflecting into variations in mesogenic behaviors and the degree
of mesomorphism between series-1 and X. A homologous series-1 of present investigation
and a nonisomeric homologous series-Y selected for comparative study are identical with
respect to the geometrical shape, three phenyl rings, two same central bridges, and left n-
alkoxy (–OR) end group for the same homolog from series to series; but, they differ with
respect to tailed end groups –OC H
and –OC H29(n), which causes difference in the
12
25(n)
14
magnitudes of molecular flexibility, which reflects in the mesogenic behaviors and the degree
of mesomorphism. Thus, the changing behaviors in mesomorphic properties and the degree
of mesomorphism depend upon varying features for the same homolog from series to series.
Following Table 4 represents some thermometric data for the series-1, X, and Y in comparative
manner.

4
4
P. K. PATEL AND R. R. SHAH
Table . Thermal stabilities in °C.
Series→
Series- (Nonlinear)
Series-X (Linear)
—
Series-Y (Nonlinear)
—
Sm-N or Sm-I
.
Commencement of smectic phase
(C –C )


C
N-I
.
.
.
Commencement of nematic phase
(C –C )
(C –C )
(C –C )






C
C
C
Total mesophase length in °C
. to .
C C
. to .
C C
. to .
C / C C
Above Table 4 indicates that,
•
Homologous series-1 of present investigation is smectogenic plus nematogenic whereas
series-X and Y chosen for comparison are only nematogenic without exhibition of smec-
togenic character.
Smectic thermal stability of present series is 110.88 and it does not stabilize even in the
monotropic condition for series-X and Y.
•
•
•
Nematic thermal stability is in decreasing order from series-1 to X to Y.
Smectic phase commences from C homolog for present series-1 but it does not com-
5
mence till the last homolog of series-X and Y.
Nematic mesophase commences earlier from C homolog of series-1 and it commences
•
•
4
from C homolog for the series X and Y in equal manner.
6
Lower total mesophase lengths adopted increasing order, whereas, upper total
mesophase lengths adopted decreasing order from series-1 to X and Y.
A nonlinear homologous series-1 of present investigation does have longer central bridge
CH=CH–COO– containing conjugated double bond as compared to linear-shaped series-X
–
containing shorter carboxylate –COO- central bridge. Therefore, the molecular rigidity and
molecular polarizability of series-1 are comparatively enhanced and more than a series-X.
Thus, enhanced molecular rigidity due to added –CH=CH– unit and molecular polarizability
due to nonlinear inverted “V” shaped molecules facilitated the layered structure in preoc-
cupied crystal lattices, through lamellar packing of molecules in rigid crystal, which under
the influence of exposed thermal vibrations maintain sliding layered molecular arrangement
on the floating surface for definite range of temperature and then residual intermolecular
attractions after smectogenic character exhibition, the same homologs manages to float the
molecules with statistically parallel orientational order to promote and facilitate nematic
mesophase formation. The intermolecular attractions and closeness though favorable, but
insufficient to maintain lamellar packing and subsequent formation and maintenance of
sliding layered molecular arrangement under identical floating condition of molecules of
series-X, due to comparatively low rigidity and low polarizability through –COO- in place
of –CH=CH–COO– and linear geometrical shape. The geometrical shape and induced
polarizability of series-1 and Y appears identical except tailed end groups, but the inter-
molecular suitable magnitudes of anisotropic forces due to wider intermolecular distance
in series-Y undergo reduction and predominated to the effect due to intermolecular polar-
izability factor of molecules of series-Y as compared to series-1, which may be affected by
unexpected and modified status of n-alkyl chain “R” of –OR and –C H
of –OC H
14
29(n)
14 29(n)
end groups together with modified lower molecular rigidity than series-1 giving rise to only
nematic phase with absence of smectic phase. The molecules of series-1 and Y are relatively
less noncoplanar as compared to series-X. Therefore, the smectic and nematic mesophases

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
45
comparatively commence earlier for a series-1 and the late for the series-X and Y in equal
manner. The longer length of –CH=CH–COO– is greater by –CH=CH– unit as compared
to identically positioned –COO- central bridge, which causes more noncoplanarity due to
a twist obtained as the oxygen atoms of the vinyl carboxy group bump into the nonbonded
adjacent hydrogen atoms of the aromatic rings. On account of these differences, the smectic-
nematic or smectic-isotropic thermal stability of series-X and Y is lower or lowest than the
corresponding smectic thermal stability of series-1. Thermal resistivity and thermal stabilities
varies with energy stored by an individual molecule as heat of formation (ꢀH). The transition
temperatures for the same homolog from series to series vary with changing magnitudes
of polarity, polarizability, effective rigidity and flexibility, dispersion forces, dipole–dipole
interaction, etc. Therefore, thermal resistivity and phase stabilization vary accordingly. Thus,
upper mesophase length and nematic thermal stabilities adopt decreasing order and lower
mesophase lengths adopt increasing order from series-1 to X to Y.
Conclusions
•
Homologous series of present investigation is predominantly nematogenic and partly
smectogenic of moderate mesophase length and thermal stabilities with thermometric
and biological importance in the benefit of mankind and middle ordered melting type.
The group efficiency order derived on the basis of (i) thermal stabilities, (ii) early com-
mencement of mesophases, and (iii) total mesophase lengths for smectic and nematic
are as under.
•
(
i) Smectic
Series-1 > series-X = series-Y
Nematic
Series-1 > series-X > series-Y
ii) Smectic
(
Series-1 > series-X = series-Y
Nematic
Series-1 > series-X = series-Y
(
iii) Total mesophase lengths
Upper: series-1 > series-X > series-Y
Lower: series-Y > series-X > series-1
Mesomorphism is very sensitive and susceptible to molecular structure as a consequence
of resulting molecular rigidity and flexibility.
Thermometric mesophase lengths and biological activity of present novel series can be
exploited in the benefit of mankind.
Present investigation supports and raises the credibility to the conclusions drawn earlier.
•
•
•
Acknowledgments
Authors acknowledge thanks to the management of the college and the Head of the Chemistry Depart-
ment, Dr. R. B. Patel of K. K. Shah Jarodwala Maninagar Science College, Ahmedabad for their valuable
cooperation in the work. 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.

4
6
P. K. PATEL AND R. R. SHAH
References
[
[
[
1] Reinitzer, F. (1888). Monatsh, 9, 421–441.
2] Hird, M., Toyne, K. J., Gray, G. W., Day, S. E., & Mc. Donell, D. G. (1993). Liq. Cryst., 15, 123–150.
3] Collings, P. J., & Hird, M. (1997). Introduction of Liquid Crystals Chemistry and Physics. Taylor and
Francis Ltd.: U.K.
[4] Marcos, M., Omenat, A., Serrano, J. L., & Ezcurra, A. (1992). Adv. Matter, 4, 285–287.
[5] Hird, M., Toyne, K. J., Gray, G. W., & Day, S. E. (1933). Liq. Cryst., 14, 741–761.
[6] Imrie, C. T. (1999). Liq. Cryst. Dimers. Struct. Bond, 95, 149–192.
[7] Gray, G. W. (1974). In: Liquid Crystals and Plastic Crystals, Gray, G. W., & Winsor, P. A. (Eds.),
Vol. 1, Ellis Horwood, Chichester, U.K., pp. 103–153.
[
[
8] Gray, G. W. (1962). Molecular Structures and Properties of Liquid Crystals. Academic Press:
London.
9] Stewart, G. T. (1974). In: Liquid Crystals and Plastic Crystals, Gray, G. W., & Winsor, P. A. (Eds.),
Chapter 6.2, Vol. 1, Taylor and Francis, U.K., pp. 308–326.
[
[
[
[
[
[
10] Gray, G. W., & Jones, B. (1954). J. Chem. Soc., 1, 2556–2562.
11] Henderson, P. A., Niemeyer, O., & Imrie, C. T. (2001). Liq. Cryst., 28, 463–472.
12] Gaikwad, P. P., & Desai, M. T. (2013). Int. J. Pharm. Res. Rev., 2(12), 40–52.
13] Demus, D. (1988). Mol. Cryst. Liq. Cryst., 165, 45–84.
14] Demus, D. (1988). Liq. Cryst., 5, 75–110.
15] (i) Suthar, D. M., & Doshi, A. V. (2013). 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). Mol. Cryst. Liq. Cryst., 575, 88–95. (iv) Bhoya, U. C., Vyas, N. N., &
Doshi, A. V. (2012). Mol. Cryst. Liq. Cryst., 552, 104–110.
[
16] Suthar, D. M., Doshi, A. A., & Doshi, A. V. (2013). Mol. Cryst. Liq. Cryst., 582, 79–87.
17] Marathe, R. B., Vyas, N. N., & Doshi, A. V. (2015). Molecular Flexibility Operated Mesomorphism.
Vol. 52, pp. 163–171. ILCPA, Scipress Ltd: Switzerland.
[
[
[
18] Marathe, R. B., & Doshi, A. V. (2015). Mol. Cryst. Liq. Cryst., 623, 1–8.
19] Dave, J. S., & Vora, R. A. (1970). In: Liquid Crystals and Ordered Fluids, Johnson, J. F., & Porter,
R. S. (Eds.), pp. 477, Plenum Press: New York.
20] Vogel, A. I. (1989). Textbook of Practical Organic Chemistry, 5th ed., pp. 946. ELBS and Longmann:
London.
21] Uhood, J. A. (2011). Int. J. Mol. Sci., 12, 3182–3190.
[
[
[
22] Lohar, J. M., & Doshi, A. V. (1993). In: Proceeding of Indian Acad. of Science-Banglore, Vol. 105,
IISC- Banglore, pp. 209–214.
[23] Ganatra, K. J., & Doshi, A. V. (2000). J. Indian Chem. Soc., 77, 322–325.
[24] Doshi, A. V., Bhoya, U. C., & Travadi, J. J. (2012). Mol. Cryst. Liq. Cryst., 552, 10–15.
[25] Bhoya, U. C., Vyas, N. N., & Doshi, A. V. (2012). Mol. Cryst. Liq. Cryst., 552, 104–110.
[26] Patel, P. K., & Shah, R. R. (2016). Mol. Cryst. Liq. Cryst., 630, 130–138.
[27] Jain, B. B., & Patel, R. B. (in press). Mol. Cryst. Liq. Cryst.