Tuning the mesomorphic properties of nonisomeric chalconyl-ester bases homologous series: The effect of tail group

Article abstract of DOI:10.1080/15421406.2016.1262686

The mesomorphic properties of nonlinear chalconyl ester homologous series can be tuned in a predictable fashion with tail groups (-OC₁₆H₃₃) substituents on the terminal side. Novel series consisted thirteen members (C₁–C₈, C₁₀, C₁₂, C₁₄, C₁₆, C₁₈). C₁ to C₅ homologues are nonliquid crystal, C₆ to C₁₄ homologues shows nematic mesophase enantiotropically, while C₁₆, C₁₈ exhibits smectic as well nematic properties. The texture of the nematic mesophase is of fan shaped, schlieren and nematic droplets type. All these compounds were characterized by elemental analyses and spectroscopic techniques such as [FTIR] and 1H Nuclear magnetic resonance [NMR] spectroscopy. The mesomorphic properties of these compoundswere observed by optical polarized light microscopy (POM) and differential scanning calorimetry (DSC).

Full text of DOI:10.1080/15421406.2016.1262686

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Tuning the mesomorphic properties of
nonisomeric chalconyl-ester bases homologous
series: The effect of tail group
Vinay S. Sharma & R. B. Patel
To cite this article: Vinay S. Sharma & R. B. Patel (2017) Tuning the mesomorphic properties of
nonisomeric chalconyl-ester bases homologous series: The effect of tail group, Molecular Crystals
and Liquid Crystals, 643:1, 40-51, DOI: 10.1080/15421406.2016.1262686
To link to this article: http://dx.doi.org/10.1080/15421406.2016.1262686
Published online: 23 Feb 2017.
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Date: 24 February 2017, At: 03:14

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
http://dx.doi.org/./..
Tuning the mesomorphic properties of nonisomeric
chalconyl-ester bases homologous series: The effect of tail
group
Vinay S. Sharma and R. B. Patel
Chemistry Department, K.K. Shah Jarodwala Maninagar Science College, Gujarat University, Ahmedabad,
Gujarat, India
ABSTRACT
KEYWORDS
Enantiotropic; liquid crystal;
nematic; smectic
The mesomorphic properties of nonlinear chalconyl ester homologous
series can be tuned in a predictable fashion with tail groups (-OC16H33)
substituents on the terminal side. Novel series consisted thirteen mem-
bers (C1–C8, C10, C12, C14, C16, C18). C1 to C5 homologues are nonliquid crys-
tal, C6 to C14 homologues shows nematic mesophase enantiotropically,
while C16, C18 exhibits smectic as well nematic properties. The texture of
the nematic mesophase is of fan shaped, schlieren and nematic droplets
type. All these compounds were characterized by elemental analyses
and spectroscopic techniques such as [FTIR] and 1H Nuclear magnetic
resonance [NMR] spectroscopy. The mesomorphic properties of these
compounds were observed by optical polarized light microscopy (POM)
and differential scanning calorimetry (DSC).
GRAPHICAL ABSTRACT
Introduction
Liquid crystals are matter in a state that has properties between those of conventional liq-
uid and solid crystals. For instance, a liquid crystal may flow like a liquid, but its molecules
may oriented in a crystal like way. [1–4]. Liquid crystals can be divided into thermotropic,
lyotropic, and metallotropic phases. Thermotropic and lyotropic liquid crystals consist mostly
of organic molecules although few minerals are also known. Presently, we have focus on ther-
motropic liquid crystals in which, phase transition into liquid crystal phase as temperature
CONTACT Vinay S. Sharma
vinaysharma@gmail.com
Science College, Gujarat University, Ahmedabad , Gujarat, India.
Chemistry Department, K.K. Shah Jarodwala Maninagar
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gmcl.
©  Taylor & Francis Group, LLC

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
41
changed [5–7]. Liquid crystals in the nematic group are most commonly used in production
of liquid crystal displays (LCD) due to their unique physical properties and wide temperature
range. In the nematic phase, liquid crystal molecules are oriented on average along a partic-
ular direction. By applying an electric or magnetic field the orientation of the molecules can
be derived in a probable approach [8–10].
A number of chalcone having reported to exhibit a broad spectrum of anti-bacterial, anti-
fungal, antiulcer, antimalarial, antitumor, anticancer, anti-inflammatory, and antitubercular
=
[11–13]. The presence of α, β-unsaturated functional group in chalcone (-CH CH-CO-)
is responsible for anti-microbial activity, which can be altered depending upon the type of
substituent present on the aromatic rings [14,15]. Thus, the object of work to synthesized
and studied the effect of chalconyl-ester linkage group and geometrical shape on meso-
morphism. Vorlander et al. reported bent-core liquid crystals and reported their mesogenic
properties [16]. Matsunaga et al. reported first time on a series of bent-core molecule, as
1,3-phenylene bis[4-(4-n-octyloxyphenyliminomethyl) benzoate] derivatives [17]. In 1996,
Niori et al. reported on ferro electricity in a smectic phase formed by bent-shaped Schiff base
derivatives in an achiral mesogen [18]. Takezoe and Takanishi et al. reported chiral nonlinear
optic effect shown in achiral bent-core molecules is due to interaction between polarity and
chirality [19]. Ros et al. studied the banana shaped mesophases synthesization is based on
the appropriate combination between rigid bent-core units with terminal side chain [20].
Subala et al. reported the same homologues series with the same core and increasing number
of chain length are responsible in the contribution of the phase sequence B6-B1-B2 [21].
Many series of liquid crystalline compounds containing heterocyclic groups have been syn-
thesized due to their usefulness in wide application electrical, optical, biological and medical
field [22,23].
In present article, we are going to present nonlinear homologous series which consisted
=
of three phenyl rings bonded through vinyl ester (-CH CH-COO-) and chalcone (-CO-
=
CH CH-) central groups and varying left n-alkoxy terminal end group (-OC16H33). Doshi
et al. synthesized and studied the molecular structure of LC property of chalconyl ester based
homologous series [24, 25]. In previous work, we have demonstrated isomeric and noniso-
meric homologues series with chalconyl ester linkage group [26,27]. Group efficiency order
and structure relation with mesomorphism will be derived.
Experimental
Synthesis
The target chalconyl-ester compounds and their derivatives were synthesized as outlined in
(Scheme-1). Trans 4-n-alkoxy cinnamic acids (A) were prepared by modified method of Dave
et al. and Vora et al. [28]. 3-(4-(hexadecyloxy) phenyl)-1-(3-hydroxy phenyl prop-2-en-1-
one) (B) was prepared by usual established method [29]. In the final step, Coupling of com-
pound (A) and (B) is done by Steglich esterification to yield final product [30]. Thus, Chal-
conyl - Ester homologue derivatives were filtered, washed with sodium bicarbonate solution,
dried and purified till constant transition temperatures using an optical polarizing micro-
scope equipped with a heating stage. Alkyl halides, 3-hydroxy acetophenone, dicyclohexyl
carbodimide (DCC), dimethyl amino pyridine (DMAP), dichloro methane, ethanol, acetone
required for synthesis were used as received except solvents which was dried and distilled prior
to use. The molecular structures of the target products and the intermediates were confirmed
by spectroscopic analysis and elemental analysis.

42
V. S. SHARMA AND R. B. PATEL
Reaction scheme
Scheme . Synthesis route of series-.
Characterization
Representative homologues series were characterised by elemental analysis, Infrared spec-
troscopy, 1H NMR spectra. IR spectra were recorded by Perkin-Elmer spectrum GX, 1HNMR
spectra were recorded on Bruker using CDCl3 as solvent. Microanalysis was performed
on Perkin-Elmer PE 2400 CHN analyzer (Table 1). Texture image of some homologues
for nematic phase were determined by miscibility method (Table 2). Transition tempera-
ture (Table 3) and LC properties (Textures) were determined using an optical polarizing
microscopy equipped with heating stage. Decomposition temperatures (Table 4) were deter-
mined using of Shimadzu DSC 60 differential Scanning Calorimeter with a heating rate of 5 to
10.0 °C min−1 in air and it was calibrated with indium (156.6 °C, 28.45 Jg−1) Holland. Ther-
=
modynamic quantities enthalpy (ꢀH) and entropy (ꢀS ꢀH/T) are qualitatively discussed.
The mesophase and transition temperatures and enthalpies for all chalconyl-ester bases liquid
crystals were determined by differential scanning calorimetry (DSC) and polarizing optical
microscopy (POM).

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
43
Table . Elemental analysis for () methoxy, () propyloxy, () butyloxy, () pentyloxy, and () hexyloxy
derivatives.
Elements % found
H
Elements % Calculated
H
Sr. no.
Molecular formula
CHO
C
O
C
O

.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.




C
HO
HO
CHO
HO
C
C
Table . Texture of nematic phase of C, C, C, C by miscibility method.
Sr. no.
Homologue
Texture

C
C
C
C
Threaded
Schlieren
Threaded
Schlieren



Analytical data
IR Spectra in cm− for heptyloxy (C), pentyloxy (C), decyloxy (C), hexadecyloxy (C),
and octadecyloxy (C) derivatives
Heptyloxy (C7): 721 Polymethylene group of (-CH2-)n of –OC7H15, 833(–C-H- def. m
di-substituted), 748 Polymethylene group of (-CH2-) of –OC16H33, 941 (–C-H- def. hydro-
carbon), 1076 and 1022(-C-O-) str, 1253, 1165 (-C-O) str in –(CH2)n chain, 1446 and 1465
=
=
(-C-H- def. in CH2), 1512 (-C C-)str, 1662 (-C O group), 1724 (-COO- ester group), 2812
=
=
and 2927 (aromatic -C-H str.), 3140, 3170 ( C-H str.), 975 (trans, -CH CH-) group.
Pentyloxy (C5): 740 Polymethylene group of (-CH2-)n of –OC5H11, 648 Polymethylene group
of (-CH2-)n of -OC16H33, 810(–C-H- def. m di-substituted), 972 (–C-H- def. hydrocarbon),
1064 (-C-O-) str, 1381 and 1230, 1157 (-C-O str in –(CH2)n chain, 1381 and 1442 (-C-H- def.
Table . Transition temperature in °C by POM.
Transition temperatures in °C
Sr. no
R = n-alkyl group
Cr
Smectic
Nematic
Isotropic













C
C
C
C
C
C
C
C
C
C
C
C
C
·
·
·
·
·
·
·
·
·
·
·
·
·
—
—
—
—
—
—
—
·
—
—
—
—
—
.
.
.
.
.
.
.
.
—
—
—
.
.
.
.
.
.
.
.
.
.
·
·
·
·
·
·
·
·
·
·
·
·
·
—
—
—
—
—
—
—
—
.
.
—
·
·
·
·
·
·
·
·
·
·
·
·
.
.
.
·
·
·
·

44
V. S. SHARMA AND R. B. PATEL
Table . Thermal stability comparison of Sm-N and N-I in series- and series-X.
Series
Series-
Series-X
—
Sm-I or Sm-N or N-Sm
Commencement of Smectic phase
.
(C - C)
C
N-I or I-N
Commencement of Nematic phase
.
(C- C)
.
(C- C)
C
C
.°C to .°C C
C
Total mesophaselength from t°C to t°C
.°C to .°C
C C
=
=
in CH2),1504 -C C-)str, 1604 and 1658 (-C O group), 1724 (-COO- ester group), 2854 and
=
2924(-C-H str in CH3), 972 (trans, -CH CH-) group.
Decyloxy (C10): 763 Polymethylene group of (-CH2-)n of –OC10H21, 640 Polymethylene
group of (-CH2-)n of –OC16H33, 833(–C-H- def. m di-substituted), 941 (–C-H- def. hydro-
carbon), 1056 (-C-O-) str, 1373 and 1303 and 1249, 1165 (-C-O str in –(CH2)n chain, 1388
=
=
and 1468 (-C-H- def. in CH2),1512 (-C C-)str, 1640 and 1660 (-C O group), 1760 (-COO-
=
ester group), 2854 and 2916 (-C-H str in CH3), 972 (trans, -CH CH-) group.
Hexadecyloxy (C16): 643 Polymethylene (-CH2-)n of –OC16H33, 640 Polymethylene group
of (-CH2-)n of –OC16H33, 833(–C-H- def. m di-substituted), 941 (–C-H- def. hydrocarbon),
1056 (-C-O-) Str, 1373 and 1303 and 1249, 1165 (-C-O str in –(CH2)n chain, 1388 and 1468
=
=
(-C-H- def. in CH2),1512, 1562 (-C C-)str, 1608 and 1661 (-C O group), 1760 (-COO- ester
=
group), 2854 and 2916 (-C-H str in CH3), 971 (trans, -CH CH-) group.
Octadecyloxy (C18):621 Polymethylene (-CH2-)n of –OC18H37, 640 Polymethylene group of
(-CH2-)n of –OC16H33, 833(–C-H- def. m di-substituted), 941 (–C-H- def. hydrocarbon),
1056 (-C-O-) str, 1373 and 1303 and 1249, 1165 (-C-O str in –(CH2)n chain, 1380 and 1462
=
=
(-C-H- def. in CH2),1512 (-C C-) str, 1604 and 1660 (-C O group), 1735 (-COO- ester
=
group), 2854 and 3024(-C-H str in CH3), 972 (trans, -CH CH-) group.
H NMR spectra in CDCl in δ ppm for methoxy (C), heptyloxy (C), octyloxy (C), decyloxy
(C), and dodecyloxy (C) derivative
Methoxy (C1): 0.88 (t, 3H, -CH3 of –C16H33), 1.26 (m, 2H n-poly methylene groups of-
OC16H33),1.75 (m, 2H, n-poly methylene groups of –OC16H33), 1.29 (p, 10 H of –OC16H33
group), 3.81 (s,-O-CH2-CH3-of –OCH3), 4.06 (t,3H,-O-CH2-CH2-of –OC16H33), 6.93-6.95
=
=
(d, 1H, J = 15.6 Hz, -CO-CH CH-), 7.53-7.55 (d, 1H, J = 15.6 Hz, -CO-CH CH-), 7.28-
=
=
7.31 (d, J = 15.2 Hz, 1H, -CH CH-COO-), 6.50 (d, J = 15.2 Hz, 1H, -CH CH-COO-),
6.94-6.92 and 7.62-7.62 (d, 4H, left side phenyl ring), 7.74 and 8.58, 8.41 (3H, central phenyl
ring), 7.62-7.62 and 6.94-6.92 (d, 4H, terminal phenyl ring).
Heptyloxy(C7): 0.88-0.90 (t, 6H, -CH3 of –OC7H15 and –OC16H33), 1.26 (m, n-poly methy-
lene groups of -OC16H33), 1.31 (q, 8H, -CH2 of –OC7H15 and –OC16H33), 1.29 (P, 10 H of
–OC7H15 and –OC16H33 group), 1.75 (m, n-poly methylene groups of –OC7H15), 3.5-3.6
(s,-OCH2-CH2-of-OC16H33), 4.06 (t,6H,-O-CH2-CH2-of –OC7H15 and -OC16H33), 7.54-7.56
=
=
(d, J = 15.6 Hz, 1H, -CO-CH CH-), 8.30-8.32 (d, J = 15.6 Hz, 1H, -CO-CH CH-), 7.62-
=
=
7.64 (d, J = 15.2 Hz, 1H, -CH CH-COO-), 6.30 (d, J = 15.2 Hz, 1H, -CH CH-COO-),
6.94-6.91 and 7.60-7.62 (d, 4H, left side phenyl ring), 7.71 and 8.56, 8.41 (3H, central phenyl
ring), 7.60-7.61 and 6.95-6.92 (d, 4H, terminal phenyl ring).

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
45
Octyloxy (C8): 0.88 (t, 6H, -CH3 of –OC8H17 and –OC16H33), 1.2-1.3 (m, n-poly methylene
groups of –OC8H17 and -OC16H33), 1.29 (P, 10 H of –OC8H17 and –OC16H33 group), 1.74-
1.76 (m, n-poly methylene groups of –OC8H17 and -OC16H33), 4.06 (t,6H,-O-CH2-CH2-of
=
–OC8H17 and –OC16H33), 6.92-6.95 (d, J = 15.6 Hz, 1H, -CO-CH CH-), 7.52-7.55 (d, J =
=
=
15.6 Hz, 1H, -CO-CH CH-), 7.28-7.31 (d, J = 15.2 Hz, 1H, -CH CH-COO-), 6.50 (d, J =
=
15.2 Hz, 1H, -CH CH-COO-), 6.94-6.90 and 7.61-7.62 (d, 4H, left side phenyl ring), 7.74 and
8.58, 8.41 (3H, central phenyl ring), 7.62-7.60 and 6.95-6.92 (d, 4H, terminal phenyl ring).
Decyloxy (C10): 0.88 (t, 6H,-CH3 of –OC10H21 and –OC16H33), 1.2-1.5 (m, n-poly methylene
groups of –OC10H21 and -OC16H33), 1.29 (P, 10 H of –OC10H21 and –OC16H33 group), 1.31
(q, 8H of 1.80 (m, n-poly methylene groups of –OC10H21 and –OC16H33), 4.06 (t,6H,-O-CH2-
=
CH2-of –OC10H21 and –OC16H33), 6.93-6.95 (d, J = 15.6 Hz, 1H, -CO-CH CH-), 7.53-7.55
=
=
(d, J = 15.6 Hz1H, -CO-CH CH-), 7.28-7.31 (d, J = 15.2 Hz, -CH CH-COO-), 6.50 (d, J
=
= 15.2 Hz, 1H, -CH CH-COO-), 6.94-6.92 and 7.62-7.62 (d, 4H, left side phenyl ring), 7.74
and 8.58, 8.40 (3H, central phenyl ring), 7.62-7.61 and 6.94-6.92 (d, 4H, terminal phenyl ring).
Dodecyloxy (C12): 0.88 (t, 6H, -CH3 of –OC12H25 and –OC16H33), 1.2-1.5(m, n-poly methy-
lene groups of –OC12H25 and -OC16H33), 1.81 (m, n-poly methylene groups of –OC12H25 and
–OC16H33), 1.29 (P, 10 H of –OC12H25 and –OC16H33 group), 1.31 (q, 8H of 1.80 (m, n-poly
methylene groups of –OC12H25 and –OC16H33), 4.06 (t, 6H,-O-CH2-CH2-of -OC12H25 and
=
–OC16H33), 6.93-6.95 (d, J = 15.6 Hz, 1H, -CO-CH CH-), 7.53-7.55 (d, J = 15.6 Hz, 1H,
=
=
-CO-CH CH-), 7.28-7.31 (d, J = 15.2 Hz, 1H, -CH CH-COO-), 6.50 (d, J = 15.2 Hz, 1H,
=
-CH CH-COO-), 6.94-6.92 and 7.62-7.62 (d, 4H, left side phenyl ring), 7.74 and 8.58, 8.41
(3H, central phenyl ring), 7.62-7.61 and 6.95-6.92 (d, 4H, terminal phenyl ring).
Result and discussion
POM investigation
Presently, we have synthesized nonlinear homologous series by the condensation of Trans
4-n-alkoxy cinnamic acid and α-3-Hydroxy benzoyl β-4ꢀ-n-hexadecyloxy phenyl ethylene
(chalcone). Here in present article, we prepared thirteen homologue (C1 to C8, C12, C14, C16,
C18) in which C1 to C5 homologues are non LCs while C6 to C18 shows LCs property at
heating and cooling condition. Mesomorphism commences in homologues series from
C6 homologue to last C18 homologue as enantiotropically manner respectively. Transition
temperatures (Table 2) determined by polarization optical microscope were plotted against
transition temperature versus the number of carbon atoms present in n-alkyl chain of the left
n-alkoxy terminal end group (-OR). The phase diagram shows Cr-I, Cr-Sm, N-I transition
curve drawn by linking like or related transition points as shown in (Fig. 1). In present case,
we have studied the effect on liquid crystalline property by geometrical shape and flexibility
due to present long chain at terminal side (-OC16H33) at right side and varying left alkoxy
side chain. Cr-I curve falling as series is increased with number of methylene unit linked in
it and ascended at dodecyloxy (C12) homologue attributable to abnormality and continued
to descend upto C18 homologue. The smectic to nematic transition curve falls in descended
manner from C16 to C18 homologue, because of increasing number of methylene units which
induce smectic mesophase. Nematic-isotropic phase transition curve descending at C7 homo-
logue and falling at C8 homologue, this is due to odd and even parity of carbon present in alkyl
chain and continued decreasing up to last C18 homologue respectively. While increasing num-
ber of carbon it behaves due to fairly abnormality from dodecyloxy to octadecyloxy derivative.

46
V. S. SHARMA AND R. B. PATEL
Figure . Phase diagram of series by POM.
The mesogenic properties are varying from homologue to homologue in same series because
of added methylene group in left side of n-alkoxy terminal side chain. The presence of odd-
even effect in (N-I) curve diminishes as series is increase beyond C18 homologue.
The absence of mesomorphism in C1 to C5 homologue, due to absence of lamellar packing
of molecules in their solid crystal lattices at solid from and after applying heating, unsuit-
able magnitudes of intermolecular anisotropic forces of lateral attractions which hinders to
maintain sliding moving layered of molecules on the surface under exposed thermal vibra-
tions at floating condition. As increasing the numbers of carbon in side chain moving of
sliding arrangement of molecules causes smectic mesophase (fan and needle) C16,C18 homo-
logue. The exhibition of nematogenic mesophase for definite range of temperature in C6 to
C18 homologue is attributed to the suitable magnitudes of anisotropic forces of intermolecu-
lar attractions due to fittest magnitudes of molecular polarity and polarizability, permanent
dipole-moment across long molecular axis with increasing chain, dispersion forces, etc. as a
consequence of favourable molecular rigidity and flexibility which facilitated statistically par-
allel orientational order of molecules in floating condition on the surface to cause nematic
mesophase (threaded and schlieren type) in the presence of thermal energy.
Texture images of comp.C10, C12, C18, and C16 are mention in Fig. 2, for C10 homologue, the
schlieren type texture image observed at 82 °C, (b) schlieren type texture of C12 homologue at
82 °C, (c) fan type texture of smectic phase observed for C18 homologue at 52 °C, (d) broken
fan texture of smectic phase of C16 homologue at 69 °C at heating and cooling conditions,
respectively.
Some LC properties evaluated from thermotropic data of presently novel series-1 and com-
pared with structurally similar analogous series X [31] and Y [32] as shown in (Fig. 3). The
geometrical shape of both the series are equal. However, the linearity of the both series are dif-
ferent with first linking group so their magnitudes of combined effects of molecular rigidity
=
and flexibility change by –CH CH- group more in series-1. Therefore magnitudes of molec-
ular rigidity and flexibility of left side chain undergo variations but flexibility at tail group
remains unaltered for the same homologue from series-1 and series X, respectively.
Figure 4 represents the space filling diagram of both the series. The trans isomer of chalcone
is form by reaction of 3-hydroxy acetophenone with 4-hexadecyloxy benzaldehyde which was

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
47
Figure . Texture of series-l observed between cross polarizers: (a) nematic phase of C homologue at
 °C; (b) nematic phase of C homologue at  °C; (c) SmC phase of C homologue at  °C, (d) SmC
phase of C homologue at  °C.
confirmed by IR. Chalcone linkage group is present in both series with unaltered flexibility at
terminal side chain group.
Some physical thermometric properties are mentioned in (Table 4) for the analogous series
under comparative study. Thermal stability of nematic is 94.37 which is lower than the series
=
X, this is due to present of –COO- central group in place of –CH CH-COO- central linkage
which effectively contribute to molecular rigidity and flexibility due to decreases in length by
=
the absence of –CH CH- unit and increases suitable magnitudes of intermolecular end to
end attractions and closeness. Thus, transition temperature and hence the thermal stability
for nematic are higher in series X as compare to series 1. However, the total mesophaselength
Figure . Structurally similar series- and series-X.

48
V. S. SHARMA AND R. B. PATEL
Figure . Space filling model of (a) series- and (b) series-X.
of series X is higher than series 1. The Sm-N thermal stability of series 1 is 73.5. An exhibition
of smectic phase in series 1, due to suitable magnitudes of anisotropic forces in presence of –
=
CH CH- causes trans isomerism which facilitate to induce intermolecular cohesions and
closeness as a consequence of favourable magnitudes of molecular rigidity and flexibility
cause by presence of long side hexadecyloxy, octadecyloxy chain at left ending side and unal-
tered terminal side chain (-OC16H33). The early or late commencement of mesomorphism
depends upon the extent of molecular noncoplanarity. The late commencement of smec-
tic phase in present synthesized series may be due to deteriorating of the lateral attractions
because of the disproportionate length to breadth ratio, rigidity in higher homologues C16,
C18. Gray et al. [32] explained that the addition of the double bond to the system increases the
length and polarizability of rod like molecules. Therefore, the greater molecular length ratio
=
and polarizability of the molecule resulting from additional –CH CH- units in the central
linkage.
DSC study
DSC is a valuable method for detecting phase transitions. The thermal behaviour of novel
homologues series were confirmed by using DSC measurement shown in (Fig. 5). Thermo-
gram is traces in both heating and cooling condition. For C18 homologue, heating condition
first endothermic peak at 47.24 °C, which indicates the presence of SmC phase shown in
texture image. That was observed by POM study. While second endothermic peak observed
at 74.21 °C, which indicates the presence of nematic phase, cooled condition again two
endothermic were traces at 44.64 °C and 72.12 °C. C7 homologue, only one significant peak is
observed at 92.18 °C, while in cooling stage it trace at 94.67 °C. In C12 homologue, endother-
mic peak observed at 88.78 °C confirmed the presence of nematic phase confirmed by POM
study while at cooled condition endothermic peak trace at nearly 90.52 °C. For C8 homo-
logue, it was observed that no smectic phase is present by POM analysis which was confirmed
by DSC measurement. One significant peak is observed at heating and cooling condition, at
heating condition endothermic peak observed at 92.18 °C and cooling condition endother-
mic peak traces at 96.10 °C, respectively. Thus, chalconyl-ester based nonlinear compound
displays lower melting type mesomorphism. In addition, presently homologues series shows
LCs property at low temperature.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
49
Figure . DSC measurement (a) C homologue (b) C homologue (c) C homologue (d) C homologue.
Transition temperature obtained by DSC analysis at heating and cooling condition and
the value of enthalpy and entropy is mention in (Table 5). Molecules of every homologue
randomly oriented in all possible directions with high order of disorder or entropy (ꢀS =
ꢀH/T) beyond isotropic temperature and the enthalpy value (ꢀH). But, at cooled condi-
tion, the same from and below isotropic temperature, the mesophase is persisted to appear
reversibly at the high temperature at observed during heating condition. The mesophase
obtained enantiotropically manner in present series is smectogenic and nematogenic,
respectively.
The proposed molecular packing of the smectic C phase is given in (Fig. 6). The arrange-
ment of molecule is nonisomeric bent type shape. This is due to the molecular packing of the
Table . Transition temperature (°C) and enthalpy (J g−) and entropy change (J g−k−) by DSC
measurement.
Homologues
or Comp.
Heating scan Cooling scan
Transition
(°C)
(°C)
ꢀH (-Jg−
)
ꢀH (Jg−
)
ꢀS(J g−k−
)
ꢀS(J g−k−
)
C18
Cr-SmC
SmC-N
N-I
.
.
>.
.
.
—
.
.
.
.
.
—
.
.
.
.
.
—
C7
Cr-N
N-I
.
>.
.
—
.
.
.
—
.
.
.
—
C12
C8
Cr-N
N-I
.
>.
.
—
.
.
.
—
.
.
.
—
Cr-N
N-I
.
>.
.
—
.
.
.
—
.
.
.
—

50
V. S. SHARMA AND R. B. PATEL
Figure . Proposed molecular packing of the Sm C phase in present series.
alkyl chains with linking groups oriented tilted way directions in smectic layers structure and
effect of flexibility to induce smectic mesophase.
Conclusions
In this article we have presented the synthesis and characterization of novel nonlinear homol-
ogous series having chalconyl-ester central group with benzene core. C1 to C5 do not exhibit
LC behaviour due to high crystallising tendency, while rest of homologues shows lower melt-
ing type mesomorphism. The group efficiency order derived on the basis of thermal stability,
early commencement of mesophase, upper and lower mesophaselength. Tail ended n-alkoxy
group can induce mesomorphism in chalconyl-ester homologous series. The mesomorphism
was confirmed by POM, DSC. Present study supported and raised the credibility to the con-
clusions drawn earlier.
Acknowledgments
The authors acknowledge thanks to Dr. R. R. Shah, principal of K. K. Shah Jarodwala Maninagar Science
College, Ahmedabad. Authors also thank to Centre of Excellence, Rajkot for the analytical and spectral
services.
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