Synthesis and characterization of rigid rode shape homologous series: Effect of tail iodo group

Article abstract of DOI:10.1080/15421406.2017.1370958

In this study, the synthesis, structural characterization andmesomorphic properties of newly thirteen calamitic rod-shaped compounds derived from chalcone and 4-n-alkoxy benzoic acid. Here we present, chalcone as central group and terminal side substituted iodo (-I) group containing homologous series. Comp.C1 displayed nonmesogenic nature, while comp.C3 to comp.C18 shows enantiotropic smectic plus nematic property except comp.C2 which show only nematic phase. It is shown that chalcone as central linking unit favors a calamitic liquid crystalline behaviour in molecules. Phase transition temperatures of present synthesised compoundswere determined by optical polarisingmicroscopy (POM), differential scanning calorimetric (DSC). Thermal stabilities for smectic and nematic mesophases are 150.18 and 163.58 respectively.

Full text of DOI:10.1080/15421406.2017.1370958

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Synthesis and characterization of rigid rode shape
homologous series: Effect of tail iodo group
Vinay S. Sharma, Anuj S. Sharma & R. B. Patel
To cite this article: Vinay S. Sharma, Anuj S. Sharma & R. B. Patel (2017) Synthesis and
characterization of rigid rode shape homologous series: Effect of tail iodo group, Molecular Crystals
and Liquid Crystals, 652:1, 158-171, DOI: 10.1080/15421406.2017.1370958
To link to this article: http://dx.doi.org/10.1080/15421406.2017.1370958
Published online: 16 Oct 2017.
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Date: 18 October 2017, At: 00:00

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –

https://doi.org/./..
Synthesis and characterization of rigid rode shape homologous
series: Effect of tail iodo group
a
b
a
Vinay S. Sharma , Anuj S. Sharma , and R. B. Patel
a
Chemistry Department, K.K. Shah Jarodwala Maninagar Science College, Gujarat University, Ahmedabad,
b
Gujarat, India; Department of Chemistry, School of Science, Gujarat University, Ahmedabad, Gujarat, India
ABSTRACT
KEYWORDS
Inthisstudy, thesynthesis, structuralcharacterizationandmesomorphic
properties of newly thirteen calamitic rod-shaped compounds derived
from chalcone and 4-n-alkoxy benzoic acid. Here we present, chalcone
as central group and terminal side substituted iodo (−I) group con-
Chalcones; liquid crystal;
nematic; smectic
taining homologous series. Comp.C displayed nonmesogenic nature,
1
while comp.C to comp.C shows enantiotropic smectic plus nematic
3
18
property except comp.C which show only nematic phase. It is shown
2
that chalcone as central linking unit favors a calamitic liquid crystalline
behaviour in molecules. Phase transition temperatures of present syn-
thesised compounds were determined by optical polarising microscopy
(
POM), differential scanning calorimetric (DSC). Thermal stabilities for
smectic and nematic mesophases are 150.18 and 163.58 respectively.
GRAPHICAL ABSTRACT
1
. Introduction
A liquid crystalline (LC) state [1] has proved its ability and importance in the benefit of
mankind in the various fields of scientific and technological applications [2–9]. Present
investigations on thermotropic liquid crystalline state have been planned with an aim to
understand and establish the effect of molecular structure on LC properties [10–14] of novel
CONTACT Vinay S. Sharma
Science College, Gujarat University, Ahmedabad, , Gujarat, India.
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
vinaysharma@gmail.com
Chemistry Department, K.K. Shah Jarodwala Maninagar
©

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
159
substances. 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 [15].
Chalcone is an important class of chemical compound and is being studied extensively
because of its significant use or application in various sectors. In the fields of biology and
biochemistry, chalcone has been claimed to be one of the compounds that plays a vital role in
anti-tumor [16], anti-inflammatory [17], and anti-malaria [18] activities. It has also been doc-
umented that the chalcone possesses a remarkable nonlinear optical (NLO) property, which
is an essential element for optical communications devices [19]. The other importance of this
compound is its high photosensitivity and thermal stability, which are used in developing var-
ious crystalline electro-optical devices [20–22]. The effects of terminally substituted group on
mesogens are considerable interest because these compounds deviate from the classical rod-
like shape [23–28].
Furthermore, chalcones are used to establish for fluorescence, polymerization process and
also for dielectric properties [29–31]. Recently, it has been noted that, among many organic
compounds reported for their second harmonic generation, chalcone derivatives are known
for their excellent blue light transmittance and good crystallisability [32–33].
In the literature studies, there are several reports of mesogenic compounds having chal-
cone linkage. Vora et al. reported a homologous series of polymers containing a chalcone
linkage [34]. Soon afterword Chudghar and his co-workers reported a homologous series
containing on ester-chalcone linkages [35]. Doshi et al. have reported chalconyl ester and
chalconyl vinyl ester linkage group inbuilt between three phenyl rings and studied the effect
on mesomorphism by substituted groups at terminal and lateral side [36–40]. Previously,
Yellamaggad et al. reported the bent-core unsymmetrical dimers in which cholesteryl ester
and chalconyl moiety are present, which enhances the biaxiality and chirality of the system
[
41]. R. Gopalakrishnan et al. reported chalcone based single crystals, growth, and compari-
son of two new enone shifted chalcones and their NLO behaviour [42]. Tandel et al. studied
the chain chalconyl polymers compounds to exhibiting threaded type nematic phases [43].
Shah et al. studied a nonlinear homologous series based on ester and chalcone linkage group
[
44]. Patel et al. reported rod type homologous series having chalconyl ester central linkage
group and hexyloxy tail group [45]. Gallardo and his coworkers reported a polycatenar liquid
crystals series based on bent shaped chalcone and cyanopyridine molecules [46]. Further-
more, S.Kumar et al. reported chalcone based LCs compounds possessing short alkyl chain at
one end and other end with variable chain lengths. These derivatives were reported to exhibit
SmC, SmA and nematic phase [47].
Recently, we have reported homologous series based on three phenyl rings bonded through
–
COO–, –CH=CH–COO– and –CO–CH=CH– linking groups as well as varying left n-
alkoxy terminal end group and a fixed tail part at right side ended group and various halogen
group [48–51]. In present investigation, we have planned to study the effects of tail iodo (−I)
group on LCs properties of present synthesized chalcone-ester series.

1
60
V. S. SHARMA ET AL.
2
. Experimental
2
.1. Materials
For present synthesized homologous series required materials: 4-hydroxy benzoic acid, alkyl
bromide (R-Br) were purchased from SRL (Mumbai), 4-hydroxy benzaldehyde and 4-iodo
acetophenone were purchased from (Sigma Aldrich), KOH (Finar Chemicals, India), N,N-
dimethyl amino pyridine (DMAP) and Dicyclohexylcarbodiimide (DCC) were purchased
from Fluka Chemie (Switzerland). The solvents were dried and purified by standard method
prior to use.
2
.2. Measurements
Melting points were taken on Opti-Melt (Automated melting point system). The FT-IR spec-
−1
tra were recorded as KBr pellet on Shimadzu in the range of 3800–600 cm . Microanaly-
sis was performed on Perkin-Elmer PE 2400 CHN analyser. The texture images were stud-
ied on a trinocular optical polarising microscope (POM) equipped with a heating plate and
1
digital camera. H NMR spectra was recorded on Bruker Advance- 400 in the range of
0
.5 ppm-16 ppm using CDCl solvent. The phase transition temperatures were measured
3
−1
using Shimadzu DSC-50 at heating and cooling rates of 10°C min . Texture image of nematic
phase were determined by miscibility method, thermodynamic quantities enthalpy (ꢀH) and
entropy (ꢀS = ꢀH/T) are qualitatively discussed. For the POM study, novel synthesized
compound is sandwiched between glass slide and cover slip and heating and cooling rate is
(2°C /min) respectively.
2.3. Synthesis
4
-n-alkoxy benzoic acids (A) prepared by reported method [52]. Chalcone (B) was prepared
by reported method [53]. Esters (D) were synthesized by a method reported in literature [54].
Thus, the chalconyl-ester homologue derivatives were filtered washed with sodium bicarbon-
ate and NaOH solution, dried and purified till constant transition temperatures is obtained.
The synthetic route to a series is mentioned in scheme 1.
... Synthesis of -n-alkoxy benzoic acid (A)
4
-n-alkoxy benzoic acid were synthesized by refluxing the mixture of 4-hydroxy benzoic acid
(1 equiv.) with corresponding n-alkyl bromides (1 equiv.) in the presence of KOH (1.5 equiv.)
and MeOH/ EtOH as a solvent [52].

... Synthesis of chalcone (B)
Chalcone (B) was prepared by usual established method reported in literature [53]. (brown-
−1
ish yellow, m.p: 167°C, Yield: 76%), IR (KBr): vmax/ cm 3441 (–OH str.-bonded), 3060
(
(
–C–H str. aliphatic alkyl group), 1660 (–C=O, group), 1580–1610 (–C=C–) aromatic, 961
1
trans, (–CH=CH–) alkene). HNMR: 9.28 (s, 1H, −OH group), 7.60 (d, 1H, J = 15.5 Hz,
–CH=CH–CO–), 8.04 (d, 1H, J = 15.5 Hz, –CH=CH–CO–), 6.58–7.42 (4H, first phenyl
ring), 7.60–7.61 (4H, second phenyl ring). Elemental analysis: calculated for C H O I: C,
15
11
2
51.44; H, 3.14; O, 9.14%; found: C, 51.41; H, 3.08; O, 9.08%.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
161
Scheme . Systematic route of target compounds (i) R-Br, KOH, MeOH, Reflux; (ii) KOH, EtOH, RT,  hr; (iii)
DCC, DMAP, DCM,  hr. stirring at RT.
... Synthesis of ester derivatives (C)
The compound has been prepared by esterification of the appropriate 4-n-alkoxy benzoic acid
(
(
A) (2.02 mmol) and chalcone (B) (0.246 g, 2.02 mmol), dicyclohexylcarbodiimide (DCC)
0.457 g, 2.22 mmol) and dimethylaminopyridine (DMAP) in catalytic amount (0.002 g,
0
.2 mmol) in dry CH Cl (DCM) (30 mL) was stirred at room temperature for 48 h. The
2 2
slightly observed white precipitate of dicyclohexyl urea is obtained which was isolated by fil-
tration and removed, while the filtrate was evaporated to dryness. The resultant crude residue
was purified by column chromatography on silica gel eluting with ethyl acetate: hexane (3:2)
[
54].
Comp.C : IR (KBr): v /cm 1 3031 (C–H str. of alkane), 602 polymethylene–(CH )-n
−
7
max
2
group of –OC H , 1660 (C=O str. of carbonyl carbon of chalconyl group), 1610 (C=C str.
7
15
of alkene in chalcone), 1760 (ester, –COO– group), 1560 (–C=C str. of aromatic ring), 1170
1
(
1
C–O str. of ether linkage), 971 (trans, –CH=CH–) group. HNMR: 0.88 (t, 3H, –OC H ),
7
15
.26 (m, 4H, –OC H ), 1.42 (t, 2H,–OC H ), 1.72 (p, 2H, -OC H ), 4.06 (t, 2H, –OC H ),
7 15 7 15 7 15 7 15
8
&
.01 (d, 1H, J = 15.1 Hz, –CH=CH–CO–), 7.58 (d, 1H, J = 15.1 Hz, –CH=CH–CO–), 7.10
8.12 (d, 4H, first phenyl ring), 7.36 & 7.85 (d, 4H, second phenyl ring), 7.61 & 7.92 (d, 4H,

1
62
V. S. SHARMA ET AL.
third phenyl ring). Elemental analysis: calculated for C H O I: C, 61.27; H, 5.10; O, 11.26%;
29
29
4
found: C, 61.22; H, 5.04; O, 11.19%.
Comp.C : IR (KBr): IR (KBr): v /cm 1 3031 (C–H str. of alkane), 732 polymethylene–
−
1
0
max
(
(
CH )- group of –OC H , 1630 (C=O str. of carbonyl carbon of chalconyl group), 1610
2
n
10 21
C=C str. of alkene in chalcone), 1740 (ester, –COO– group), 1560 (–C=C str. of aromatic
1
ring), 1170 (C–O str. of ether linkage), 971 (trans, –CH=CH–) group. HNMR: 0.88 (t, 3H,
–
OC H ), 1.26 (m, 10H, –OC H ), 1.42 (t, 2H,–OC H ), 1.72 (p, 2H, -OC H ), 4.06
10 21 10 21 10 21 10 21
(
t, 2H, –OC H ), 8.01 (d, 1H, J = 15.1 Hz, –CH=CH–CO–), 7.58 (d, 1H, J = 15.1 Hz,
1
0
21
–
CH=CH–CO–), 7.10 & 8.11 (d, 4H, first phenyl ring), 7.34 & 7.82 (d, 4H, second phenyl
ring), 7.61 & 7.92 (d, 4H, third phenyl ring). Elemental analysis: calculated for C H O I: C,
32
30
4
6
3.48; H, 4.95; O, 10.58%; found: C, 63.43; H, 4.91; O, 10.51%.
−1
Comp.C : IR (KBr): vmax/cm 3031 (C–H str. of alkane), 693 polymethylene–(CH )-
1
2
2
group of –OC H , 1660 (C=O str. of carbonyl carbon of chalconyl group), 1611 (C=C
n
12 25
str. of alkene in chalcone), 1750 (ester, –COO– group), 1510 (–C=C str. of aromatic ring),
1
1
170 (C–O str. of ether linkage), 971 (trans, –CH=CH–) group. HNMR: 0.88 (t, 3H, –
OC H ), 1.26 (m, 14H, –OC H ), 1.42 (t, 2H,–OC H ), 1.72 (p, 2H, -OC H ), 4.06
12
25
12 25
12 25
12 25
(
t, 2H, –OC H ), 8.01 (d, 1H, J = 15.1 Hz, –CH=CH–CO–), 7.58 (d, 1H, J = 15.1 Hz,
1
2
25
–
CH=CH–CO–), 7.11 & 8.14 (d, 4H, first phenyl ring), 7.34 & 7.85 (d, 4H, second phenyl
ring), 7.61 & 7.91 (d, 4H, third phenyl ring). Elemental analysis: calculated for C H O I: C,
34
34
4
6
4.46; H, 5.37; O, 10.11%; found: C, 64.42; H, 5.32; O, 10.06%.
−1
Comp.C : IR (KBr): IR (KBr): vmax/cm 3030 (C–H str. of alkane), 610 polymethylene
1
8
–
(CH )- group of –OC H , 1660 (C=O str. of carbonyl carbon of chalconyl group), 1610
2
n
18 37
(
C=C str. of alkene in chalcone), 1760 (ester, –COO– group), 1530 (–C=C str. of aromatic
1
ring), 1170 (C–O str. of ether linkage), 970 (trans, –CH=CH–) group. HNMR: 0.88 (t, 3H,
–
OC H ), 1.26 (m, 24H, –OC H ), 1.29 (m, 4H, -OC H ), 1.42 (t, 2H,–OC H ), 1.72
7 15 18 37 18 37 18 37
(
(
p, 2H, -OC H ), 4.06 (t, 2H, –OC H ), 8.01 (d, 1H, J = 15.1 Hz, –CH=CH–CO–), 7.58
1
8
37
18 37
d, 1H, J = 15.1 Hz, –CH=CH–CO–), 7.11 & 8.12 (d, 4H, first phenyl ring), 7.36 & 7.86 (d,
H, second phenyl ring), 7.61 & 7.92 (d, 4H, third phenyl ring). Elemental analysis: calculated
for C H O I: C, 66.49; H, 7.06; O, 8.86%; found: C, 66.45; H, 6.97; O, 8.79%.
4
40
51
4
3
. Result and discussion
Here in present investigation, we have synthesized newly chalconyl-ester based homologous
series contain varying left alkoxy (−OR) side chain and iodo (−I) group substituted at right
tail part. In the present article, we have study the effect of linkage group and varying alkoxy
side chain on mesomorphic behaviour of liquid crystalline compounds. A newly chalconyl-
ester homologous series of liquid crystalline (thermotropic) property determined from con-
ꢀ
densation of dimeric 4-n-alkoxy benzoic acids and chalcone (α-4-hydroxy phenyl β-4 -iodo
benzoyl ethylene) is synthesized and evaluated their some thermometric data to compare
mesomorphic behaviours and the molecular structure through molecular rigidity and flexibil-
ity. The phase behaviour of all new synthesised compounds has been investigated by polaris-
ing optical microscope (POM) and confirm by using differential scanning calorimetry (DSC)
analysis.
3.1. POM investigation
We have studied comprehensively the effect of linking group as well as alkyl aliphatic chain
length to form mesogens having calamitic rod type shape. It has been proven that varying

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
163
Table . Transition temperature in °C by POM.
Transition temperatures in C
Sr no
R = n-alkyl group
−OCH (C )
Cr-I
Cr-SmC
SmC-N
N-I

.
—
—
—
—
—
·
—
—








−OC H (C )
·
·
·
·
·
·
·
·
·
·
·
·
—
·
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
·
·
·
·
·
·
·
·
·
·
·
·



−OC H (C )
.
.
.
.
.
.
.
.
.
.
.
·



−OC H (C )
·
·



−OC H (C )
·
·



−OC H (C )
·
·



−OC H (C)
·
·




−OC H (C)
·
·


−OC H (C )
·
·
  







−OC H (C )
·
·
  
−OC H (C )
·
·
  
−OC H (C )
·
·
  

−OC H (C )
·
·
  
(Cr = Solid Crystal, SmC = Smectic C phase, Nm = Nematic phase, Iso = Isotropic phase)
length of alkyl chain in alkoxy part (−OR) effect on their mesomorphic property. Here, in
present investigation, we have synthesized and study the effect of chalcone (–CH=CH–CO)
group in presence of ester (–COO–) group with terminal iodo (−I) substituted on mesogenic
property. In present series-1, we have prepared total thirteen compounds from small alkyl side
spacer C (−OCH ) to higher alkyl side spacer C (−OC H ) in presence of three benzene
1
3
18
18 37
core as rigid part. The sample was sandwiched between untreated glass plate and a cover slip to
form a thin film to study the LC textures under POM analysis. The observed data derived from
DSC and POM study complemented to each other. All the synthesized compounds, except
comp.C displayed mesogenic property in enantiotropically manner. Conversely, the type of
1
the mesomorphic property depends upon the number of carbon atoms present in the aliphatic
side chain in alkoxy (−OR) group. Comp.C shows non liquid crystal property, this is due to
1
the short alkyl spacer methoxy (−OCH ) group present in alkoxy side chain, as a result the
3
crystallising tendency of comp.C is high and upon on heating condition it directly transform
1
liquid state without exhibiting any LCs property. Smectic mesophase starts from comp.C to
3
C , while nematic mesophase start from comp.C to C in present series-1. The transition
18
2
18
temperature of present series is listed below in Table 1.
The plot of transition temperatures versus the number of carbon atoms present in the
alkoxy side chain showing Cr-M/I, SmC-N and N-I phase behaviour curve shown in Figure 1.
The phase diagram shows descending tendency form lower homologue (C ) to higher homo-
1
logue (C ). The transition curve of Cr-M/I showing decreasing tendency from comp.C to
18
1
C homologue and increases at comp.C and again descends upto last homologue (C ). Odd-
7
8
18
even effect is present in Cr-M/I and SmC-N transition curve due to presence of odd-even par-
ity of methylene group present at C and C homologue [55]. The transition curve of SmC-
7
8
N transition curve decrease upto C homologue and slightly increase at comp.C and then
7
8
continued to descending upto last homologue. N-I transition curve starts with decreasing
tendency upto comp.C and then increased at comp.C and again decreased at comp.C and
6
7
8
reaching maxima at comp.C with overall falling tendency upto last homologue (C ). In N-I
10
18
transition cure, odd-even effect is seen at comp.C to C and comp.C to C respectively. It can
5
6
7
8
be observed that, as the methylene group increases in side alkoxy tail group (−OR), the linear-
ity and polarizability of the molecules increase which increases the flexibility of the molecules

1
64
V. S. SHARMA ET AL.
to induce mesomorphism at lower temperature. The decreasing tendency of transition tem-
perature from lower alkyl spacer to higher alkyl spacer depends on the flexibility of molecules
caused by number of methylene group (–CH -) present in alkoxy side chain (−OR).
2
The exhibition of nematic phase in present series attributed to the disalignment of
molecules of an angle less than ninety degree under the externally exposed thermal vibra-
tions of suitable magnitudes which matches with internal energy stored in a molecule (ꢀH)
as related to the suitable magnitudes of anisotropic forces of intermolecular end to end
attractions, as a consequence of molecular rigidity and flexibility, which favorably arranges
molecules to float on the surface in statistically parallel orientational order to maintain molec-
ular two dimensional array [56].

... Textural study
The solid samples held between an untreated glass slide and a coverslip were heated to their
isotropic phase and cooled slowly. In Figure 2, comp.C shows typical SmC pattern at 151.0°C
6
on heating condition. Comp. C displayed needle like texture image of SmC at 148.0°C on
8
heating condition. Comp. C shows schlieren type texture pattern of nematic phase at 132.0°
14
on cooling condition while compound C exhibits textural pattern of SmC phase at 134.0°C
10
on cooling condition. In present series, mesogenic property observed at heating and cooling
condition respectively. Figure 3 indicates the phase sequence of comp.C10 on heating con-
dition, SmC phase observed at 134.0°C while applying further heating, its transform into
nematic phase at 147.0°C and with continued it became isotropic at 158.0°C, this phase
sequence again reappeared in cooling condition as well.

... Comparative study
Some LC properties evaluated from thermotropic data of presently investigated novel series-1
with compared with structurally similar reported analogues series-A [57] as mentioned below
Figure 4. The geometrical shape of both series-1, -A are calamitic rod type having three phenyl
ring and two linking groups. Presence chalcone (–CH=CH–CO–) linking group and iodo
substituted terminal part is common in both homologous series, however they differ with
Figure . Phase diagram of series-.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
165
first linkage group with respect to each other. The left terminally alkoxy (−OR) group hav-
ing varying alkyl side chain from lower homologue (C ) to higher homologue (C ). Linking
1
18
group is one of the factors to exhibiting the smectic phase instead of a nematic phase in syn-
thesized target compounds. The ester linking group in series-1 favors the lamellar packing due
to the dipole–dipole interaction which ultimately generated the smectic phase [58] as com-
pared to series-A which having vinylester group. Presently synthesized compounds follow
Figure . Photomicrograph of optical texture of (a) comp.C at .°C (heating); (b) comp. C at .°C


(
heating); (c) comp.C at .°C (cooling); (d) comp.C at .°C (cooling).


Figure . Phase sequence of comp.C .


1
66
V. S. SHARMA ET AL.
the calamitic LCs behaviour displays nematic and smectic property. The molecular length of
series-A is more as compare to series-1 due to presence of ethylene (–CH=CH–) part in cin-
namate (–CH=CH–COO–) linkage group create difference in its molecular length to breadth
ratio resulting into difference in polarity as well as polarizability of molecules [59].
In comparison to previously reported symmetrical three phenyl rings based chalcone ester
series, present symmetrical three phenyl ring based chalconyl ester series display LCs prop-
erty from lower chain alkyl spacer to higher chain alkyl spacer with good thermal stability.
Presence of iodo (−I) group at terminal part increases thermal stability of mesophase because
it is big in size more polarizable due to the electrons on this atom which are loosely held and
far from the nucleus [60]. These newly synthesized materials follow the typical calamitic LCs
behaviour displayed smectic and nematic phase. The ball-stick model of both the series are
given in below Figure 5 which indicate the geometrical shape of the molecules in both series.
Increasing methylene (–CH -) units in n-alkyl side chain at alkoxy (−OR) side terminal
2
group increases the molecular length, permanent dipolement, dispersion forces, molecular
Figure . Structurally similar analogous series-, -A.
Figure . Ball stick model of present series-, -A.
Table . Average thermal of series- and series-A in °C.
Series
Series-
Series-A
SmC-N
N-I
.
.
.
.
Total temperature range
°C to °C
C C
C
°C to °C
C C
C
(
SmC + N)
Commencement of smectic phase
Commencement of nematic phase
C
C

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
167
Figure . Temperature range of phase transition in series-, -A.
polarity and polarizability due to presence iodo (−I) group at right tail part. Consequently,
variations occur in intermolecular adhesion forces of appropriate magnitudes that exhibiting
nematic mesophase in comp. C to C member in present series-1. Presence of oxygen atom
2
18
in carboxy (–COO–) group in the molecules of the series-1 will bump into the nonbonded
side of the adjacent hydrogen of the aromatic ring, thereby causing considerable strain on the
molecule. This will cause some twist around the carbonyl bond and force the benzene ring
out of the plane of the molecule and broadening the molecule [61].

... Thermal stability
Table 2 shows the average thermal stabilities and temperature range of newly synthesized
homologous series-1 compared with series-A. The SmC–N thermal stability of series-1 is
1
1
50.18°C which is lower as compare to series-A. Thermal stability of N–I phase of series-1
63.58°C which is again lower as compare to series-A. It can be noted that, thermal stability
Figure . Proposed mechanism of present series-.

1
68
V. S. SHARMA ET AL.
Figure . DSC thermograms of compound (a) comp.C ; (b) comp.C on heating and cooling cycles.


of previously reported series-A is higher as compared to series-1 this is due to the presence of
cinnamate linking group which having ethylene (–CH=CH–) part more as compare to ester
group in series-1.
The temperature range of SmC-N, N-I and (Sm+N) phase transition is shown in Figure 6.
It is clearly seen that, total temperature range of (Sm+N) in series-A is higher as compare
to series-1. In series-1, comp.C to C shows good total temperature range (Sm+N) phase
14
18
as compare to other member of present series. Mesophase length of higher homologoues in
series-1 is higher as compare to other member of present series-1 and series-A. Figure 7 rep-
resents the proposed mechanism to induce SmC mesophase transform into nematic phase in
present calamitic rod-shaped series.
Figure . DSC thermograms of compound (a) comp.C ; (b) comp.C ; (c) comp.C on heating and cooling



cycles.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
169
−
− −
Table . Transition temperature (°C) and enthalpy (J g ) and entropy change (J g k ) by DSC
measurement.
ꢀ
(−Jg )
H
ꢀH
(Jg
ꢀS
(−J g
ꢀS
−
−
− −
− −
Comp.
Transition
Heating scan(°C)
Cooling scan(°C)
)
k
)
(J g
k
)
C7
Cr-Cr’
Cr’-SmC
SmC-N
N-I
Cr-Cr’
Cr’-SmC
SmC-N
N-I
Cr-Cr’
Cr’-SmC
SmC-N
N-I
Cr-Cr’
Cr’-SmC
SmC-N
N-I
.
.
.
>.
.
.
.
>.
.
.
.
>.
.
.
.
>.
.
.
.
.
.
.
.
—
.
.
.
—
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
—
.
.
.
—
.
.
.
—
.
.
.
—
.
—
C10
C18
C14
C3
.
.
.
.
.
.
.
.
.
.
—
.
.
.
—
.
.
.
—
.
.
.
—
.
.
.
—
.
.
.
—
.
.
.
—
.
.
.
.
.
.
.
.
.
Cr-Cr’
Cr’-SmC
SmC-N
N-I
.
.
.
—
(Cr-Cr’= solid to solid crystal; Cr’-SmC = solid to SmC; SmC-N = SmC to nematic; N-I = nematic to isotropic)
3
.2. DSC analysis
The phase transition temperatures and enthalpies were measured by carrying out DSC
thermal analysis. All compounds are thermally stable as confirmed by the reproducibility
of thermograms on several heating and cooling cycles. In Figure 8, comp.C exhibits three
7
endothermic peaks at 100.08°C, 142.61°C and 156.21°C in heating cycle, which corre-
spondence to the presence of crystal to crystal, crystal to SmC and SmC-N phase. That
was also confirmed by using POM analysis. While on cooling condition, these exothermic
peaks were trace again at 100.02°C, 142.08°C and 156.12°C. Comp. C10 displays three
endothermic peak at 101.12°C, 141.28°C and 158.97°C during heating cycle, while on
cooling cycle, it appears at 102.12°C, 142.02°C and 160.09°C which was also confirmed
by POM analysis which indicates the mesophase appeared is SmC and nematic type. In
Figure 9, comp.C shows two sharp endothermic peaks at 102.81°C and 118.21°C on heat-
18
ing cycle which reveals with POM analysis. On cooling cycle, again these two exothermic
peaks traced at 109.67°C and 120.91°C. Comp.C14 shows two sharp endothermic peaks
at 115.68°C and 136.96°C in heating condition while on cooling condition it appears
at 114.38°C and 138.16°C. It reveals with POM result. The phase transition tempera-
tures, enthalpy and entropy values for the present synthesized series are summarized in
Table 3.
4
. Conclusion
A new calamitic rod type homologous series of chalcone-derived LCs compounds possessing
iodo group at one end and other end with variable chain lengths. The C member of present
1
series shows nonliquid crystalline (NLCs) behaviour due to presence of short alkyl spacer at
terminal side chain while comp.C to C displays smectic as well as nematic phase expect
2
18
comp.C which shows only nematic mesophase. Presently synthesized chalconyl-ester based
2

1
70
V. S. SHARMA ET AL.
homologous series having iodo (−I) substituent at terminal side shows SmC and nematic
phase with good thermal stability.
Acknowledgement
Authors acknowledge thanks to Dr. R. R. Shah, principal and management of K. K. Shah Jarodwala
Maninagar Science College, Ahmedabad. Authors are also thankful to NFDD Centre for providing ana-
lytical and spectral services.
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