Synthesis and mesomorphic properties of calamitic shaped molecules with chalconyl-ester and lateral fluoro substituents

Article abstract of DOI:10.1080/15421406.2017.1412580

In this study we have synthesized a new class of compounds incorporating of chalcones and laterally substituted fluoro group. A series of new chalcones with five aromatic rings is synthesized and characterised by elemental analyses and spectroscopic techniques such as Fourier transform infrared [FT-IR] and proton magnetic resonance magnetic resonance [¹H NMR] spectroscopy. The mesomorphic properties of these compounds were observed by optical polarized light microscopy (POM) and confirmed by differential scanning calorimetry (DSC). It is found that all the prepared materials display enantiotropic LCs phases except first three homologue in present series. The lower homologues (n = 4 to 12) display SmC and nematic phase while, in higher homologues (n = 14 to 18) only SmC phase were seen in heating and cooling condition.

Full text of DOI:10.1080/15421406.2017.1412580

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Synthesis and mesomorphic properties of
calamitic shaped molecules with chalconyl-ester
and lateral fluoro substituents
Vinay S. Sharma, Anuj S. Sharma, Rajesh H. Vekariya & R. B. Patel
To cite this article: Vinay S. Sharma, Anuj S. Sharma, Rajesh H. Vekariya & R. B. Patel
(2017) Synthesis and mesomorphic properties of calamitic shaped molecules with chalconyl-
ester and lateral fluoro substituents, Molecular Crystals and Liquid Crystals, 658:1, 32-44, DOI:
10.1080/15421406.2017.1412580
To link to this article: https://doi.org/10.1080/15421406.2017.1412580
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MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
https://doi.org/./..
Synthesis and mesomorphic properties of calamitic shaped
molecules with chalconyl-ester and lateral fluoro substituents
Vinay S. Sharmaa, Anuj S. Sharmab, Rajesh H. Vekariyab, and R. B. Patela
aChemistry Department, K. K. Shah Jarodwala Maninagar Science College, Gujarat University, Ahmedabad,
Gujarat, India; bDepartment of Chemistry, School of Science, Gujarat University, Ahmedabad, Gujarat, India
ABSTRACT
KEYWORDS
Chalcones; liquid crystal;
nematic; smectic
In this study we have synthesized a new class of compounds incorpo-
rating of chalcones and laterally substituted fluoro group. A series of
new chalcones with five aromatic rings is synthesized and characterised
by elemental analyses and spectroscopic techniques such as Fourier
transform infrared [FT-IR] and proton magnetic resonance magnetic res-
onance [1H NMR] spectroscopy. The mesomorphic properties of these
compounds were observed by optical polarized light microscopy (POM)
and confirmed by differential scanning calorimetry (DSC). It is found
that all the prepared materials display enantiotropic LCs phases except
first three homologue in present series. The lower homologues (n = 4
to 12) display SmC and nematic phase while, in higher homologues (n =
14 to 18) only SmC phase were seen in heating and cooling condition.
GRAPHICAL ABSTRACT
1. Introduction
Study of liquid crystalline state (LC) is a multidisciplinary subject useful to the mankind
and industrial applications through scientist, technologists and technocrats [1–4] due to its
unique property to flow as liquid and optical properties as crystals. Calamitic molecules of
conventional and unconventional liquid crystalline materials have been intensively examined
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
33
for scientific and technological potential applications such as sensing materials, optoelectronic
display materials and biological active molecules [5–10].
A number of chalcone having reported to exhibit a broad spectrum of anti-bacterial,
antifungal, antiulcer, antimalarial, antitumor, anticancer, anti-inflammatory and antituber-
cular activity [11]. It is believe that 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 [12]. To the best of our
knowledge, liquid crystalline materials based on chalconyl central linking group are rarely
–
–
=
–
reported in literature. It has been observed that CO CH CH linkage is less conducive
to mesomorphism as compared to CH N , COO , N N , CH CH COO linkages
group because of the presence of non-linearity and angle strain arising from the presence of
–
= – –
– – = – –
=
–
–
– =
–
–
=
–
keto ( C O) group [13]. Surprisingly, when CO CH CH linkage is linked with another
linking group it becomes conductive to exhibits mesophase. In the literature studies, there are
several reports of mesogenic compounds having chalcone linkage. Furthermore, chalcones
are used to develop for fluorescence, polymerization process and dielectric properties [14].
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 [15]. R.Gopalakrishnan et al. reported chalcone based single crystals, growth,
and comparison of two new enone shifted chalcones and their NLO behaviour [16]. Tandel
et al. studied the chain chalconyl polymers compounds to exhibiting threaded type nematic
phases [17]. Vinyl esters linkage group have been well known for last decades of years, Vora et
al. reported binary mixtures of cinnamate esters exhibit a wide range of smectic and nematic
mesophase [18]. Doshi et al. reported various homologous series based on chalconyl and vinyl
ester linkage group and studied the effect on mesomorphism [19–21]. Sadashiva et al. reported
the synthesis and mesomorphic properties of some ester of trans-4-n-alkoxy cinnamic acid
and trans-4-n-alkoxy-α-methyl cinnamic acid with branched chain alkyl tails exhibiting fer-
roelectric and anti-ferroelectric phases [22]. Prajapati et al. studied some homologous series
consisted cinnamate linkage group and show its effect on mesomorphic properties of liquid
crystalline compounds [23–24]. Patel et al. prepared unsymmetrical cyclohexanone derived
bischalcones which displays monotropic nematic phase [25]. Recently, Bhoya et al. reported
a calamitic rod type homologous series containing vinyl ester and azomethine linkage groups
[26–28]. Shah et al. studied a nonlinear homologous series based on ester and chalcone link-
age group [29]. Patel et al. reported rod type homologous series having chalconyl ester central
linkage group and hexyloxy tail group [30]. Gallardo and his coworkers reported a polycatenar
liquid crystals series based on bent shaped chalcone and cyanopyridine molecules [31]. Yahya
et al. reported a series of azo-ester mesogens containing liquid crystalline acrylate having dif-
ferent terminal groups. They reported –OCH3, -OC2H5 and –OCH3 substituted compounds
exhibited greater mesophase stability as compare to halogen (-F, -Cl, -Br) [32]. Furthermore,
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 [33]. Polyimide derived from chalcones with terminal dimethacrylate
or epoxy chains and their polymers have been used for LC photo alignment studies [34, 35].
Recently, our research team reported different chalconyl ester based linear and nonlinear
homologues series and observed the effect of increasing alkyl spacer at terminal group on
mesomorphism [36–40]. The present investigation is aimed to the synthesis and character-
ization of some new chalcones with five phenyl rings having varied alkyl chain (n = 1 to
8, 10, 12, 14, 16, 18) while other end of the molecule is fixed by fluorine group. Compre-
hensive literature search of unsymmetrical chalconyl-ester derivatives based calamitic LCs
with five benzene rings have so far not been reported. Therefore, these newly synthesized

34
V. S. SHARMA ET AL.
unsymmetrical chalconyl-ester materials will help in understanding the structure-property
relationship in the growing list of chalcone-based liquid crystalline materials.
2. Experimental
2.1. General
For the synthesis of target compounds in present newly homologous series, the following
materials were used: 4-hydroxy benzoic acid, 4-hydroxy benzaldehyde were purchased from
SRL, (Mumbai), Alkyl halides (R-Br) were purchased from Lancaster, (England), 3-fluoro
benzoic acid was purchased from (Sigma Aldrich), Anhydrous K2CO3, KOH, 4-hydroxy ace-
tophenone was purchased from (SRL, Mumbai, India), DCC (Dicyclohexyl carbodimide)
was purchased from Fluka Chemie (Switzerland), Dimethyl amino pyridine DMAP (4,4’-
dimethylamino pyridine) was purchased from Finar chemicals (India), Dichloro methane,
Ethanol, MeOH, 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. Represen-
tative homologous series were characterised by elemental analysis, Infrared spectroscopy, 1H
NMR spectra. IR spectra were recorded by Perkin-Elmer spectrum GX, 1HNMR spectra were
recorded on Bruker (400 MHz) using CDCl3 as solvent. Microanalysis was performed on
Perkin-Elmer PE 2400 CHN analyser. Texture image of nematic phase were determined by
using miscibility method. Transition temperature and LC properties (Textures) were deter-
mined using an optical polarising microscopy (POM) equipped with heating stage attached
with camera. Decomposition temperatures were determined using of Shimadzu (DSC) dif-
ferential Scanning Calorimeter with a heating rate of 5°C to 10.0°C min−1.
2.2. Synthesis of compounds in present series
... Synthesis of -n-alkoxy benzoic acid (a)
4-n-alkoxy derivatives of benzoic acid were prepared method reported by Dave and Vora [41].
... Synthesis of Methyl--hydroxy benzoate (a)
Equimolar proportion of p-hydroxy benzoic acid and absolute methanol shacked well in pres-
ence of two drops of concentrated H2SO4 and reaction mixture was refluxed for two to three
hours. Then reaction mixture was dumped into ice, and allowed it to settle down. Solid white
precipitate of methyl-4-hydroxy benzoate is obtained. Product was filtered, washed, dried and
then purified by alcohol. Fine crystals are obtained (M.P.126°C, yield 72%) [42].
... Synthesis of -(methoxy carbonyl) phenyl ’-n-alkoxy benzoate (a)
4-(methoxy carbonyl) phenyl 4’-n-alkoxy benzoate has been prepared by esterification of the
appropriate 4-n-alkoxy benzoic acid (2a) (2.02 mmol) and methyl-4-hydroxy benzoate (3a)
(2.02 mmol), dicyclohexyl carbodiimide (DCC) (2.22 mmol) and dimethylaminopyridine
(DMAP) in catalytic amount (0.2 mmol) in dry CH2Cl2 (DCM) (60 ml) was stirred at room
temperature for 48 h. The white precipitate of DCU is obtained which was isolated by filtra-
tion and remove, while the filtrate was evaporated to dryness. The resultant crude residue was
purified by column chromatography on silica gel eluting with methanol: chloroform as eluent
(2:4) [43].
Comp. 3a4: IR (KBr): vmax/ cm−1 3033 (C H str.), 679 polymethylene group of OC4H9
–
–
1
–
–
–
–
chain group, 1740 ( COO group), 1240 (C O str.). HNMR: 0.88 (t, 3H, OC4H9), 1.45

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
35
–
–
–
–
(sex, 3H, OC4H9), 1.76 (q, 2H, OC4H9), 4.06 (t, 2H, OC4H9), 3.82 (s, 3H, OCH3), 7.12
& 8.01 (d, 4H, first phenyl ring), 7.38 & 8.11 (d, 4H, second phenyl ring). Elemental analysis:
calculated for C19H20O5: C, 69.51; H, 6.09; found: C, 69.41; H, 5.91; O, 5.89%.
... Synthesis of -((’-n-alkoxy benzoyl) oxy) benzoic acid (a)
4-((4’-n-alkoxy benzoyl) oxy) benzoic acid were prepared by dissolving (compound 3b) in
ethanol (40 ml) and 10% aq. KOH (2 ml) was added. The resultant mixture was heated at
reflux for 6 to 7 hours then cooled to room temperature, poured into ice cold water (80 ml)
and then acidified with dil.HCl. The crude product obtained by filtration was recrystallized
by using MeOH/ DCM [44].
−1
–
–
–
Comp. 4a4: IR (KBr): vmax/ cm , 3071 (C H str.), 3301 ( OH of carboxylic group), 1680
=
–
–
(C O str. of carboxylic group), 1750 ( COO group), 648 polymethylene group of OC4H9
1
–
–
–
group. HNMR: 0.88 (t, 3H, OC4H9), 1.44 (sex, 2H, OC4H9), 1.72 (q, 2H, OC4H9), 4.07
–
–
(t, 2H, OC4H9), 10.8 (s, 1H, COOH group), 7.11 & 8.01 (d, 4H, first phenyl ring), 7.58 &
8.23 (d, 4H, second phenyl ring). Elemental analysis: calculated for C18H18O5: C, 68.78; H,
5.73%; found: C, 68.69; H, 5.68%.
... Synthesis of -formyl phenyl -fluoro benzoate (a)
4-formyl phenyl 3-fluoro benzoate (5a) was synthesized by taking the mixture of 4-hydroxy
benzaldehyde (2 mmol.) with 3-fluoro benzoic acid (2 mmol.) in DCC (2 mmol), DMAP in
catalytic amount (0.2 mmol) in dry DCM (40 ml) was stirred at room temperature for 48 h.
The white precipitate of DCU is obtained which was isolated by filtration and remove, while
the filtrate was evaporated to dryness. The resultant crude residue was purified by column
chromatography on silica gel eluting with ethyl acetate: hexane as eluent (3:2) [45].
... Synthesis of -(-(-hydroxy phenyl)--oxoprop--en--yl) phenyl -fluoro
benzoate (chalcone) (a)
Chalcone (6a) was prepared by usual established method reported in literature [46]. (yellow,
Yield: 66%), IR (KBr): vmax/ cm−1 3430 ( OH str.-bonded), 3079 ( C H str.), 1667 ( C O,
–
– –
– =
1
–
–
– = –
group), 1730 ( COO , group), 1580–1610 ( C C ) aromatic, 962 (trans, alkene). HNMR:
–
–
=
–
–
5.28 (s, 1H, OH group), 7.46 (d, J = 15.4 Hz, 1H, CH CH CO ), 8.01 (d, J = 15.4 Hz,
–
=
–
–
1H, CH CH CO ), 6.86, 8.05 (4H, first phenyl ring), 7.32, 7.78 (4H, second phenyl ring),
7.45-7.48, 7.80, (d, 4H, third phenyl ring). Elemental analysis: calculated for C22H15O4F: C,
72.92; H, 4.14; found: C, 72.69; H, 4.04.
... General procedure for the synthesis of final target compounds (a)
The compound has been prepared by esterification of the appropriate compound (4a) (2.02
mmol) and compound (6a) (0.246 g, 2.02 mmol), dicyclohexyl carbodiimide (DCC) (0.457 g,
2.22 mmol) and dimethylaminopyridine (DMAP) in catalytic amount (0.002 g, 0.2 mmol) in
dry CH2Cl2 (DCM) (40 ml) was stirred at room temperature for 48 h. The slightly yellowish
white precipitate of DCU is obtained which was isolated by filtration and remove, while the
filtrate was evaporated to dryness. The resultant crude residue was purified by column chro-
matography on silica gel eluting with methanol: chloroform as eluent (1:4) [45]. The synthesis
route of target compounds was mention in below scheme 1 and 2.
7a5: IR (KBr): vmax/cm−1 3066 (C-H str. of alkane), 1601 (C C str. of alkene in chalcone),
=
– = –
–
–
–
–
1630 ( C O ), 1730 ( COO group), 992 (C H bending of alkene), 1170 (C O str. of
1
ether linkage of pentyloxy group), 791 (polymethylene group of –OC5H11). HNMR: 0.90
–
–
(t, 3H, J = 6.2 Hz, CH3 of polymethylene –OC5H11), 1.31-1.33 (sex, 4H, OC5H11), 1.76(q,
–
–
2H, OC5H11), 4.06 (t, J = 6.5 Hz, 2H, OC5H11), 8.01 (d, 1H, J = 15.5 Hz, olefinic

36
V. S. SHARMA ET AL.
–
=
–
=
–
–
H, CH CH-CO), 7.57 (d, 1H, J = 15.5 Hz, olefinic H, CH CH CO ), 7.14 (m, 4H,
Ar-H), 7.32 (m, 4H, Ar-H), 7.56-8.29 (m, 6H, Ar-H), 7.52 (m, 4H,Ar-H).Elemental analysis:
calculated for C41H33O8F: C, 76.87; H, 5.15; found: C, 76.81; H, 5.08%.
7a6: IR (KBr): vmax/cm−1 3063 (C H str. of alkane), 1610 (C C str. of alkene in chal-
cone), 1660 ( C O ), 1760 ( COO group), 992 (C H bending of alkene), 1170 (C O
str. of ether linkage of hexyloxy group), 762 (polymethylene group of –OC6H13). HNMR:
–
=
– = –
–
–
–
–
1
–
–
–
0.88 (t, 3H, J = 6.5Hz, CH3 of polymethylene OC6H13), 1,29-1.43 (m, 8H, OC6H13),
–
–
1.76(q, 2H, OC6H13), 4.06 (t, J = 6.5 Hz, 2H, OC6H13), 8.01 (d, 1H, J = 15.5 Hz, olefinic
–
=
–
–
=
–
–
H, CH CH CO), 7.56 (d, 1H, J = 15.5 Hz, olefinic H, CH CH CO ), 7.14 (m, 4H, Ar-
H), 7.32, 7.80 (m, 4H, Ar-H), 7.56-8.29 (m, 6H, Ar-H), 7.52, 8.21 (m, 4H,Ar-H).Elemental
analysis: calculated for C42H35O8F: C, 77.06; H, 5.35%; found: C, 76.98; H, 5.31%.
7a10: IR (KBr): vmax/cm−1 3062 (C H str. of alkane), 1601 (C C str. of alkene in chal-
–
=
– = –
–
–
–
–
cone), 1640 ( C O ), 1760 ( COO group), 991 (C H bending of alkene), 1170 (C O str.
of ether linkage of decyloxy group), 772 (polymethylene group of –OC10H21). 1HNMR: 0.88
–
–
–
(t, 3H, J = 6.5Hz, CH3 of polymethylene OC10H21), 1,26-1.31 (m, 12H, OC10H21), 1.76(p,
–
–
–
2H, OC10H21), 4.06 (t, J = 6.5 Hz, 2H, OC10H21), 1.41 (t, 2H, OC10H21), 8.02 (d, 1H, J =
–
=
–
–
=
–
–
15.5 Hz, olefinic H, CH CH CO), 7.57 (d, 1H, J = 15.5 Hz, olefinic H, CH CH CO ),
7.14 (m, 4H, Ar-H), 7.32 (m, 4H, Ar-H), 7.56-8.29 (m, 6H, Ar-H), 7.52 (m, 4H,Ar-H). Ele-
mental analysis: calculated for C51H53O8F: C, 78.46; H, 6.79%; found: C, 78.42; H, 6.73%.
2.3. Reaction scheme
Scheme . Synthetic route of some derivatives of present synthesized series. Reagent and conditions: (i) R-
Br, KOH, MeOH, Reflux; (ii) MeOH, conc.HSO, Reflux; (iii) -n-alkoxy benzoic acid (a), DCC, DMAP, DCM, rt,
 h; (iv) KOH, ethanol, Reflux; (v) DCC, DMAP, DCM, rt,  h.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
37
Scheme . Synthetic of unsymmetrical chalcone target compounds a to a; reagent and conditions: (vi)
KOH, EtOH, rt,  h; (vii) DCC, DMAP, DCM, rt,  h.
3. Result and discussion
Herein, we have synthesized newly chalconyl-ester based homologous series contain lateral
–
fluoro substituted side group and varying left alkyl chain in alkoxy ( OR) group. In the present
investigation, we study the effect of linkage group and varying flexibility on mesomorphic
behaviour of liquid crystalline compounds. Two main complementary instrument techniques
were employed, namely DSC and polarized optical microscopy (POM) for the detailed study
of thermal and optical properties.
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 altering the
length of alkyl chain in left alkoxy group (-OR), effect on their mesogenic property. Here, in
present study, we have synthesized and study the effect of chalcone group in presence of other
ester group on mesogenic behaviour of fluoro substituents compounds. In present series, we
–
have prepared total thirteen compounds from small spacer 7a1 ( OCH3) to higher spacer
–
7a18 ( OC18H37) in presence of five phenyl ring joint by four linking groups. The sample
was sandwiched between untreated glass plate and a cover slip to form a thin film to study
the LC textures under POM study. The observed data derived from DSC and POM study

38
V. S. SHARMA ET AL.
Table . Transition temperature in °C by POM.
R = n-alkyl
Transition temperatures in C
Cr-SmC SmC-N
Sr.no
group
Cr-I
N-I













a
a
a
.
.
.
—
—
—
—
—
—
—
·
—
—
—
—
—
—
—
—
—
—
—
—
·
—
—
—
—
—
—
·
·
a
a
a
a
a
a
a
a
a
a
—
—
—
—
—
—
—
—
—
—
—
·
.
.
.
.
.
.
.
—
.
.
.
.
.
.
.
.
.
.
·
.
.
.
.
.
.
.
.
.
·
·
·
·
·
·
·
·
·
·
·
·
·
·
·
·
·
·
—
—
—
·
—
—
—
·
·
—
—
·
·
·
(Cr = solid crystal; Sm = smectic phase; N = nematic phase; I = isotropic phase).
complemented to each other. All the synthesized compounds, except for three derivatives
(7a1 to 7a3) exhibit LC property in enantiotropically manner. However, the type of the LC
property depends on the number of carbon atoms in the aliphatic side chain spacer at left
alkyl chain. Nematic mesophase commences from 7a4 to 7a12 homologous, while smectic
mesophase start from 7a5 to 7a18 homologous in present series. The transition temperature
of present series is listed below in Table 1.
The plot of transition temperatures versus the number of carbon atoms in the alkoxy side
chain showing Cr-M/I, Sm-N and N-I phase transition curve (Figure 1). Cr-M/I transition
curve showing falling tendency from 7a1 to 7a5 homologue and increases at 7a6 and 7a8 homo-
logue and then gradually decreases at 7a18 homologue. Odd-even effect is present in Cr-M/I
transition curve. Sm-N transition curve exhibits decreasing tendency from 7a5 to 7a12 homol-
ogous without exhibition of any odd-even effect. N-I transition curve initially descended
at 7a5 homologue, ascended 7a6 homologue and then continued to falling upto last 7a18
homologue with exhibition of odd-even effect. It can be noted that, as the methylene
Figure . Phase diagram of series.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
39
Figure . Photomicrograph of optical texture of (a) comp. a at .°C (heating); (b) comp. a at .°C
(cooling); (c) comp. a at .°C (cooling); (d) comp. a at .°C (cooling).
group increases in side alkoxy group(-OR), the linearity and polarizability of the molecules
increase which increases the flexibility of the molecules to induce mesomorphism at lower
temperature.
The exhibition of nematic phase in higher homologue in present series attributed to the
disalignment of molecules of an angle less than ninety degree under the externally exposed
thermal vibrations 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 favor-
ably arranges molecules to float on the surface in statistically parallel orientational order to
maintain molecular two dimensional array [20]. It can be seen that, a nematogenic mesophase
appeared from and beyond isotropic temperature (N-I), the molecules are randomly oriented
in all possible directions with high order of disorder in unexpected manner or with high
entropy (ꢀS = ꢀH/T).
The inexhibition of mesogenic behaviours by 7a1, 7a2 and 7a3 homologue is due to the
low magnitudes of dispersion forces and dipole-dipole interactions which make unsuitable
magnitudes of intermolecular anisotropic forces of cohesion and closeness. Instead, it induces
high crystallising tendency due to presence of short alkyl spacer chain length and abruptly
breaks the crystal lattices under thermometric condition and sharply transform into isotropic
liquid from crystalline state without passing through an intermediate state of existence
LC [47]
... Textural study
The solid samples held between an untreated glass slide and a coverslip were heated to their
isotropic phase and cooled slowly. As shown in Figure 2, comp.7a7 exhibits SmC pattern at
47.0°C on heating condition. Comp. 7a12 exhibit schlieren type texture image having four
brush of nematic phase at 76.0°C on cooling condition. Comp. 7a16 shows threaded type tex-
ture pattern of nematic phase at 42.0˚ on cooling condition while in compound 7a18 exhibits
nematic droplets at 38.0°C on cooling condition.

40
V. S. SHARMA ET AL.
Figure . Space filling diagram of present series.
... Thermal stability of mesophase
The space-filling diagram suggests the energy minimize in present series is mention in below
Figure 3. The geometrical shape of series is calamitic rod type, five phenyl ring joint via three
–
–
–
–
=
–
ester ( COO ) and one chalcone ( CO CH CH ) linking group with terminally unaltered
fluoro substituents and varying alkyl side chain at left terminal part throughout the entire
series from lower homologue (7a1) to higher homologue (7a18). Linking group is one of the
factors to exhibiting the smectic phase instead of a nematic phase in synthesized target com-
pounds. The ester linking group favors the lamellar packing due to the dipole–dipole inter-
action which ultimately generated the smectic phase [48]. Presently synthesized compounds
follow the typical calamitic LCs behaviour where lower member shows nematic and smectic
mesophase while the higher members compounds display only smectic phases.
In comparison to previously reported symmetrical and unsymmetrical four phenyl rings
chalcone ester [33, 49], present unsymmetrical five phenyl rings chalconyl ester based homol-
ogous series shows LCs property at lower temperature and early commencement of mesogenic
property from lower side chain C4 to higher chain C18. Introducing one more phenyl ring
with ester linkage group and -meta substituted fluoro (-F) group decrease the transition tem-
perature of mesophase. These newly synthesized materials follow the typical calamitic LCs
behaviour where lower homologous displayed smectic and nematic phase while the higher
ones exhibit only smectic phases. As the molecular structure of presently five ring based chal-
conyl ester is different than other previously reported chalconyl liquid crystalline series, it is
not logical to compare their mesophase behaviour.
Increasing methylene (–CH2–) units in n-alkyl side chain at alkoxy side terminal group
increases the molecular length, permanent dipolement, dispersion forces, molecular polarity
and polarizability due to presence of highly electronegative fluorine group at right terminal
part. Subsequently, changes occur in intermolecular adhesion forces of appropriate magni-
tudes that exhibiting nematic mesophase in comp. 7a4 to 7a12 in present series. Increasing
the length of molecular due to presence of five linking groups to exhibiting smectic as well as
nematic mesophase. Presence of oxygen atom in carboxy (–COO) group in the molecules of
the series 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

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
41
Table . Average thermal and mesophase stabilities of series in °C.
Series
Comp. a to a
SmC-N
N-I
.
.
SmC-I
.
. to .
C C
Total temperature range
(SmC+N)
carbonyl bond and force the benzene ring out of the plane of the molecule and broadening
the molecule [50].
Table 2 shows the average thermal stabilities and mesophase range of newly homologous
series (7a1 to 7a8, 7a10, 7a12, 7a14, 7a16, 7a18). The N–I thermal stability of series is 113.28°C.
Thermal stability of SmC–N phase is 85.0°C. However, the thermal stability of SmC-N phase
is 59.33°C. From the Table 3, it indicates that the total temperature range of (SmC + N)
mesophase of present series is 58.0°C (7a5) and 16.0°C (7a18) respectively. The thermal sta-
bility of N-I phase is higher as compare to SmC-I and SmC-N phase, this result indicate that
the stability of nematic phase in present series is higher as compare to smectic phase. It can
be noted that, the temperature range of SmC-N phase transition is higher as compare to N-I
and SmC-I phase. The temperature range of homologue 7a7 is higher as compare to other
homologous in present series.
3.2. DSC analysis
The phase transition temperatures and enthalpies were measured by carrying out DSC ther-
mal analysis. All compounds are thermally stable as confirmed by the reproducibility of
thermograms on several heating and cooling cycles. In Figure 4, compound 7a8 exhibits
three endothermic peaks at 39.21°C, 52.54°C and 75.81°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 POM analysis. While on cooling condition, again these exothermic
peaks were traced at 77.62°C, 53.23°C and 42.66°C. Compound 7a7 exhibits two endother-
mic peak at 43.17°C and 87.46°C during heating cycle, while on cooling cycle, it appears
Table . Transition temperature (ºC) and enthalpy (J g−) and entropy change (J g−k−) by DSC
measurement.
Heating
scan (ºC)
Cooling
scan (ºC)
Comp.
C
Transition
ꢀH (−Jg−
)
ꢀH (Jg−
)
ꢀS (−J g−k−
)
ꢀS (J g−k−
)
Cr-Cr’
Cr’-SmC
SmC-N
N-I
Cr-SmC
SmC-N
N-I
Cr-Cr’
Cr’-SmC
SmC-N
N-I
Cr-Cr’
Cr’-SmC
SmC-N
N-I
.
.
.
>
.
.
>
.
.
.
>
.
.
.
>
.
.
.
—
.
.
—
.
.
.
—
.
.
.
.
.
.
—
.
.
—
.
.
.
—
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
—
.
.
—
.
.
.
—
.
C
C
.
.
.
.
.
.
.
C
—
.
.
.
—
—
.
.
—
.
.
—
.
.
—
.
.
.

42
V. S. SHARMA ET AL.
Figure . DSC thermograms of compound (a) a; (b) a; (c) a; (d) a on heating and cooling cycles.
at 40.98°C and 89.12°C which was also confirmed by POM analysis which indicates the
mesophase appeared is SmC and nematic type. Compound 7a6 shows three endothermic
peaks at 35.67°C, 56.25°C and 93.46°C on heating cycle which reveals with POM study. On
cooling cycle, again these exothermic peaks traced at 94.62°C, 51.20°C and 32.48°C. Com-
pound 7a12 shows three endothermic peaks at 15.98°C, 46.67°C and 75.98°C in heating condi-
tion while on cooling condition it appears at 75.88°C and 45.21°C. On POM study, it confirms
the presence of nematic phase in heating and cooling condition. The phase transition tem-
peratures, 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 possess-
ing fluoro group at one end and other end with variable chain lengths. The lower member
7a1 to 7a3 shows nonliquid crystalline behaviour due to presence of short alkyl spacer. The
smaller alkoxy chain compounds exhibit SmC and nematic phase while higher alkoxy side
chain compounds display only SmC phase. The LC phase of higher homologous displayed at
lower temperature in present synthesized series.
Acknowledgement
The authors thank Dr. R. R. Shah, principal and management of K. K. Shah Jarodwala Maninagar Sci-
ence College, Ahmedabad. The authors are also thankful to NFDD Centre for providing analytical and
spectral services.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
43
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