λ-Shaped mesogens based on chalconyl ester core having variable side chain: Synthesis and characterisation

Article abstract of DOI:10.1080/15421406.2018.1515699

In present study, we have synthesized two newly chalconyl-ester core LCs having variable side chain and fixed disubstituted butoxy group at another terminal end. All this compounds were well characterized by elemental analysis, FT-IR, ¹H NMR. The mesomorphic properties of these compounds were observed by optical polarized light microscopy (POM) and also confirmed by using differential scanning calorimetry (DSC) and X-ray diffraction pattern (XRD). Detailed XRD investigation endorses the presence of the nematic phase in higher angle region and SmC phase in lower angle region. In addition, it is found that all the prepared materials display enantiotropic LCs phases except first four members in series-1 and first member in series-2. Thermal stability of SmC and nematic phase of series-1 is higher as compare to series-2. To get more insights, the DFT based HOMO, LUMO studies are carried out which supports intramolecular charge transfer interactions and stability in this class of mesogens.

Full text of DOI:10.1080/15421406.2018.1515699

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: https://www.tandfonline.com/loi/gmcl20
λ-Shaped mesogens based on chalconyl ester
core having variable side chain: Synthesis and
characterisation
Vinay S. Sharma, Deepak Suthar & Anuj S. Sharma
To cite this article: Vinay S. Sharma, Deepak Suthar & Anuj S. Sharma (2018) λ-
Shaped mesogens based on chalconyl ester core having variable side chain: Synthesis
and characterisation, Molecular Crystals and Liquid Crystals, 665:1, 100-118, DOI:
10.1080/15421406.2018.1515699
To link to this article: https://doi.org/10.1080/15421406.2018.1515699
Published online: 13 Feb 2019.
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MOLECULAR CRYSTALS AND LIQUID CRYSTALS
018, VOL. 665, NO. 1, 100–118
2
https://doi.org/10.1080/15421406.2018.1515699
k-Shaped mesogens based on chalconyl ester core having
variable side chain: Synthesis and characterisation
a
b
c
Vinay S. Sharma , Deepak Suthar , and Anuj S. Sharma
a
Department of Chemistry, Faculty of Basic and Applied Sciences, Madhav University, Sirohi, Rajasthan,
b
India; Department of Physics, Faculty of Basic and Applied Sciences, Madhav University, Sirohi,
Rajasthan, India; Department of Chemistry, School of Science, Gujarat University, Ahmedabad,
c
Gujarat, India
ABSTRACT
KEY WORDS
Chalcone; enantiotropic;
nematic; smectic C
In present study, we have synthesized two newly chalconyl-ester
core LCs having variable side chain and fixed disubstituted butoxy
group at another terminal end. All this compounds were well charac-
1
terized by elemental analysis, FT-IR, H NMR. The mesomorphic prop-
erties of these compounds were observed by optical polarized light
microscopy (POM) and also confirmed by using differential scanning
calorimetry (DSC) and X-ray diffraction pattern (XRD). Detailed XRD
investigation endorses the presence of the nematic phase in higher
angle region and SmC phase in lower angle region. In addition, it is
found that all the prepared materials display enantiotropic LCs
phases except first four members in series-1 and first member in ser-
ies-2. Thermal stability of SmC and nematic phase of series-1 is
higher as compare to series-2. To get more insights, the DFT based
HOMO, LUMO studies are carried out which supports intramolecular
charge transfer interactions and stability in this class of mesogens.
CONTACT Vinay S. Sharma
vinaysharma3836@gmail.com
Department of Chemistry, Faculty of Basic and Applied
Science, Madhav University, Sirohi, Rajasthan, India.
ß 2018 Taylor & Francis Group, LLC

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
101
1. Introduction
Thermotropic liquid crystals are an important class of self-organized molecular entities
which are in dynamic motion yet possessing long range orientational order [1–2].
Thermotropic LC molecule consists a core, which is usually containing a rod type linker
that linked with aromatic ring by different linker unit and tail part which are either
straight alkyl or alkoxy chains whose terminal unit is obviously a polar substituent to
providing flexibility to stabilize the molecular alignment. Base on the type of the sub-
stituents and their combinations, both nematic and smectic mesophases may be formed
[3–5]. Study of liquid crystalline state is a multidisciplinary subject and useful to man-
kind and various industrial applications [6–9] due to its unique property to flow as
liquid as well as the optical behaviour as crystals.
Till date, a number of chalcone having reported to exhibit a broad spectrum of anti-
bacterial, antifungal, antiulcer, antimalarial, antitumor, anticancer, anti-inflammatory
and antitubercular activity [10–11]. It is believe that the presence of a, b-unsaturated
functional group in chalcone (-CH ¼ CH-CO-) is mainly responsible for anti-microbial
activity, which can be altered depending upon the type of substituent present on the
aromatic rings [12]. It has been observed that -CO-CH ¼ CH- linkage is less conducive
to display mesomorphism as compared to -CH ¼ N-, -COO-, -N ¼ N linkages group
because of the presence of non-linearity and angle strain arising from keto (-C ¼ O)
group [13–15]. Surprisingly, when -CO-CH ¼ CH- linkage is linked with another link-
ing group it becomes more conductive to induces thermally stable LCs properties. The
literature report indicates that the mesogenic compounds having chalcone linkage
group [16–21].
Doshi et al. 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 [22–24]. Gallardo and his coworkers reported polyca-
tenar liquid crystals series based on bent shaped chalcone and cyanopyridine molecules
[25]. 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 [26]. Recently, Zhao et al. reported five new
series of azo benzene liquid crystals involving chalcone and ester linkage group having
thiophene, naphthalene and ferrocene core [27].
In this present work, we have synthesized two newly series of thermotropic mesogens
based on three phenyl rings with variable side chain at one end and fixed di-substituted
butoxy group at right terminal end. We have studied the basic structural understanding
of a new class of k-shape three-ring based LCs compounds with ester and chalcone link-
age group at the molecule bend having variable alkyl side chain in alkoxy group (-OR)
and also studied the effect of polar nitro group on mesomorphic behaviour in series-2.
The LCs properties are studied by using POM, DSC and PXRD analysis. Furthermore,
density functional theory (DFT) based HOMO, LUMO studies are carried out which
supports charge transfer interactions in presently synthesized LCs compounds. Recently,
our research group have reported various calamitic and bent type homologous series
which consisted three phenyl rings bonded through vinyl ester (-CH ¼ CH-COO-) or
ester (-COO-) and chalcone (-CO-CH ¼ CH-) linking units [28–31].

1
02
V. S. SHARMA ET AL.
2
. Experimental
.1. Materials
For present synthesized homologous series required materials: 4-hydroxy acetophenone,
-hydoxy benzoic acid, 3,4-dihydroxy benzaldehyde, 3,4-dihydroxy 5-nitro benzaldehyde
2
4
were purchased from (Sigma Aldrich). N, N-dimethyl amino pyridine (DMAP) and
Dicyclohexyl carbodiimide (DCC) was purchased from (Fluka Chemie, Switzerland).
The alkyl bromides were purchased from (S.R.L. Chemicals, Mumbai, India). 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
ꢀ
1
spectra were recorded as KBr pellet on Shimadzu in the range of 3800-600 cm .
Microanalysis was performed on Perkin-Elmer PE 2400 CHN analyser. The texture
images were studied on a trinocular optical polarising microscope (POM) equipped
1
with a heating plate and digital camera. H NMR was recorded on a 400 MHz in
Bruker Advance in the range of 0.5 ppm-16 ppm using CDCl solvent. The phase transi-
3
tion temperatures were measured using Shimadzu DSC-50 at heating and cooling rates
ꢁ
ꢀ1
of 10 C min . The samples were heated from room temperature to 550˚C at 10˚C/
min. X-ray diffraction (XRD) measurements were performed on a Rigaku-Ultima IV
powder diffractometer equipped with a Cu ka source (k ¼ 1.5418 A˚ and 1.6 kW, X-ray
tube with applied voltage and current values as 40 kV and 30 mA power) and also
Philips X’PERT MPD.
2
.2.1 Synthesis of Methyl-4-hydroxy benzoate (1a)
Equimolar proportion of p-hydroxy benzoic acid and absolute methanol shacked well in
presence of two drops of concentrated H SO and reaction mixture was refluxed for
2
4
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 79%) [31].
2
.2.2 Synthesis of Methyl-4-n-alkoxy benzoate (1b)
Methyl-4-n-alkoxy benzoate(3b) were prepared by alkylation of Methyl-4-hydroxy
benzoate (3b) with alkyl bromide (R-Br) in MeOH (C to C ) and EtOH (C to C18)
1
8
10
and reflux at 3 to 4 hrs. and then dump into ice-cold water to get final Methyl-4-n-
alkoxy benzoate (3b) derivatives [31].
2
.2.3 Synthesis of 4-n-alkoxy benzoic acid (1c)
-n-alkoxy benzoic acids (3c) were prepared by dissolving comp.3b in ethanol (40 ml)
and 10% aq. KOH (2 ml) was added. The resultant mixture was heated at reflux for 6 to
4

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
103
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 [32].
ꢀ
1
Comp.1C : IR (KBr): v /cm , 3021 (C-H str.), 3301 (-OH of carboxylic group),
4
max
1
650 (C ¼ O str. of carboxylic group), 648 polymethylene group of –OC H group.
4
9
1
HNMR: 0.88 (t, 3H, –OC H ), 1.44 (sex, 2H, -OC H ), 1.72 (q, 2H, -OC H ), 4.07
4
9
4
9
4
9
(
t, 2H, -OC H ), 10.2 (s, 1H, -COOH group), 7.11 & 7.92 (d, 4H, first phenyl ring).
4 9
ꢀ
1
Comp.1C : IR (KBr): v /cm , 3071 (C-H str.), 3308 (-OH of carboxylic group),
8
max
1
680 (C ¼ O str. of carboxylic group), 1710 (-COO- group), 641 polymethylene group
1
of –OC H group. HNMR: 0.88 (t, 3H, –OC H ), 1.26-1.30 (m, 8H, -OC H ), 1.44
8
17
8
17
8
17
(
sex, 2H, -OC H ), 1.72 (q, 2H, -OC H ), 4.07 (t, 2H, -OC H ), 10.8 (s, 1H, -COOH
8 17 4 9 8 17
group), 7.12 & 7.91 (d, 4H, first phenyl ring).
2.2.4 Synthesis of (E)-3-(3,4-dibutoxy phenyl)-1-(4-hydroxy phenyl) prop-2-en-1-one
(
2b) (chalcone). Chalcone (2b) was prepared by usual established method reported in lit-
ꢀ
1
erature [31]. (Yellow, Yield: 74%), IR (KBr): vmax/cm 3460 (-OH str.-bonded), 3079-
2
920 (-C-H str.), 1667 (-C ¼ O, group), 1610 (alkene) aromatic, 1280 (-O-CH - ether
2
1
linkage), 962 (trans, alkene). HNMR: 0.90 (t, 6H, -CH of disubstituted –OC H group),
3
4
9
1
4
.46 (q, 4H, -disubstituted –OC H group), 1.74 (p, 4H, -disubstituted –OC H group),
4 9 4 9
.06 (t, 4H, -disubstituted –OC H9 group), 6.64 (s, 1H, -OH group), 7.58 (d,
4
J ¼ 15.4 Hz, -CO-CH ¼ CH-), 8.01 (d, J ¼ 15.4 Hz, -CO-CH ¼ CH-), 6.86 (d, 4H, first
phenyl ring), 7.21 (d, 4H, second phenyl ring).
2.2.5 Synthesis of (E)-3-(3,4-dibutoxy-5-nitrophenyl)-1-(4-hydroxy phenyl) prop-2-en-
1
-one
(
3b) (chalcone). Chalcone (3b) was prepared by usual established method reported in lit-
ꢀ
1
erature [31]. (Brown, Yield: 68%), IR (KBr): vmax/cm 3461 (-OH str.-bonded), 3079-
2
1
930 (-C-H str. aliphatic alkyl group), 1660 (-C ¼ O, group), 1610 (-C ¼ C-) aromatic,
740 (-COO- group),1460 (-NO str.), 1280 (-O-CH - ether linkage), 962 (trans,
2
2
1
alkene). HNMR: 0.90 (t, 6H, -CH of disubstituted –OC H group), 1.46 (q, 4H,
3
4
9
-
-
disubstituted –OC H group), 1.74 (p, 4H, -disubstituted –OC H group), 4.06 (t, 4H,
4 9 4 9
disubstituted –OC H group), 6.64 (s, 1H, -OH group), 7.81 (d, J ¼ 15.4 Hz, -CO-
4
9
CH ¼ CH-), 8.13 (d, J ¼ 15.4 Hz, -CO-CH ¼ CH-), 6.88 (d, 4H, first phenyl ring), 7.83,
.62 (s, 2H, second phenyl ring).
7
2
.2.6 General procedure for the synthesis of final target compounds (2C)
The final target compounds (2C) has been prepared by esterification of the appropriate
compound (1c) (2 mmol) and compound (2b) (2 mmol), dicyclohexyl carbodiimide
(
(
DCC) (2.22 mmol) and dimethylaminopyridine (DMAP) in catalytic amount
0.2 mmol) in dry CH Cl (DCM) (30 ml) was stirred at room temperature for 28 h. The
2
2
slightly yellowish precipitate of DCU is obtained which was isolated by filtration and
remove, while the filtrate was evaporated to dryness. The resultant crude residue was

1
04
V. S. SHARMA ET AL.
purified by column chromatography on silica gel eluting with ethyl acetate: hexane as
eluent (3:2) [32].
ꢀ
1
Comp.2C : IR (KBr): vmax/cm
3460 (-OH str.-bonded), 3041 (-C-H str.), 1660
1
(
-C ¼ O, group), 1610 (alkene) aromatic, 1220 (-O-CH - ether linkage), 963 (trans,
2
1
alkene), 751 polymethylene group of –OC H . HNMR: 0.90 (t, 6H, -CH of disubsti-
4
9
3
tuted –OC H group), 1.46 (q, 4H, -disubstituted –OC H group), 1.74 (p, 4H, -disub-
4
9
4
9
stituted –OC H group), 4.06 (t, 4H, -disubstituted –OC H9 group), 3.81 (s, 3H,
4
9
4
-
disubstituted –OC H group), 7.58 (d, J ¼ 15.4 Hz, -CO-CH ¼ CH-), 8.01 (d,
4
9
J ¼ 15.4 Hz, -CO-CH ¼ CH-), 6.88 (d, 4H, first phenyl ring), 7.53 (d, 4H, second phenyl
ring), 7.06 (d, 2H, third phenyl ring), 7.21 (s, 1H, third phenyl ring).
ꢀ
1
Comp.2C : IR (KBr): v /cm , 3020 (C-H str.), 1660 (-C ¼ O group), 1740 (-COO-
5
max
group), 1280 (-O-CH - ether linkage), 960 (trans –CH ¼ CH-), 648 polymethylene
2
1
group of –OC H group. HNMR: 0.88-0.90 (t, 9H, -CH of disubstituted –OC H and
5
11
3
4
9
–
OC H group), 1.30 (m, 4H, -OC H group), 1.46 (q, 4H, -disubstituted –OC H9
5 11 5 11 4
group), 1.74 (p, 6H, -disubstituted –OC H group and –OC H ), 4.06 (t, 6H, -disubsti-
4
9
5
11
tuted –OC H group and –OC H ), 3.81 (s, 3H, -disubstituted –OC H group), 7.58
4
9
5
11
4
9
(
d, J ¼ 15.4 Hz, -CO-CH ¼ CH-), 8.01 (d, J ¼ 15.4 Hz, -CO-CH ¼ CH-), 6.88 (d, 4H, first
phenyl ring), 7.53 (d, 4H, second phenyl ring), 7.06 (d, 2H, third phenyl ring), 7.21 (s,
H, third phenyl ring).
1
ꢀ
1
Comp.2C : IR (KBr): v /cm , 3023 (C-H str.), 1640 (-C ¼ O group), 1730 (-COO-
3
max
group), 1240 (-O-CH - ether linkage), 960 (trans –CH ¼ CH-), 641 polymethylene
2
1
group of –OC H group. HNMR: 0.88-0.90 (t, 9H, -CH of disubstituted –OC H and
4
9
3
4
9
–OC H group), 1.46 (q, 4H, -disubstituted –OC H group), 1.74 (p, 6H, -disubstituted
3 7 4 9
–
OC H group and –OC H ), 4.06 (t, 6H, -disubstituted –OC H group and –OC H ),
4
9
3
7
4
9
3
7
7
.58 (d, J ¼ 15.4 Hz, -CO-CH ¼ CH-), 8.01 (d, J ¼ 15.4 Hz, -CO-CH ¼ CH-), 6.87 (d, 4H,
first phenyl ring), 7.53 (d, 4H, second phenyl ring), 7.06 (d, 2H, third phenyl ring), 7.21
s, 1H, third phenyl ring).
(
2
.2.7 General procedure for the synthesis of final target compounds (3C)
The final target compounds (3C) has been prepared by esterification of the appropriate
compound (3b) (2 mmol) and compound (1c) (2 mmol), dicyclohexyl carbodiimide
(
(
DCC) (2.22 mmol) and dimethylaminopyridine (DMAP) in catalytic amount
0.2 mmol) in dry CH Cl (DCM) (30 ml) was stirred at room temperature for 28 h. The
2
2
slightly yellowish 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) [32].
ꢀ
1
Comp.3C : IR (KBr): vmax/cm
3079 (-C-H str.), 1660 (-C ¼ O, group), 1612
1
(
-C ¼ C-) aromatic, 1760 (-COO- group), 1460 (-NO str.), 1280 (-O-CH - ether link-
2
2
1
age), 961 (trans, alkene), 668 (polymethylene group of –OC H ). HNMR: 0.90 (t, 6H,
4
9
-
CH of disubstituted –OC H group), 1.46 (q, 4H, -disubstituted –OC H group), 1.74
3 4 9 4 9
(
p, 4H, -disubstituted –OC H group), 3.81 (s, 3H, -OCH ), 4.06 (t, 4H, -disubstituted
4 9 3
–
OC H group), 6.64 (s, 1H, -OH group), 7.82 (d, J ¼ 15.4 Hz, -CO-CH ¼ CH-), 8.14 (d,
4
9

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
105
J ¼ 15.4 Hz, -CO-CH ¼ CH-), 7.10 (d, 4H, first phenyl ring), 7.54 (d, 4H, second phenyl
ring), 7.61, 7.82 (s, 2H, third phenyl ring).
ꢀ
1
Comp.3C : IR (KBr): vmax/cm
3079 (-C-H str.), 1660 (-C ¼ O, group), 1612
4
(
-C ¼ C-) aromatic, 1750 (-COO- group), 1463 (-NO str.), 1260 (-O-CH - ether
2
2
1
linkage), 668 (polymethylene group of –OC H ), 961 (trans, alkene). HNMR: 0.88-
4
9
0
.90 (t, 6H, -CH3 of disubstituted –OC H9 and –OC H9 group), 1.46 (q, 6H,
4 4
-
disubstituted –OC H and –OC H group), 1.74 (p, 6H, -disubstituted –OC H
4 9 4 9 4 9
and –OC H group), 4.06 (t, 6H, -disubstituted –OC H and –OC H group), 7.83
4
9
4
9
4
9
(
d, J ¼ 15.4 Hz, -CO-CH ¼ CH-), 8.14 (d, J ¼ 15.4 Hz, -CO-CH ¼ CH-), 7.11 (d, 4H,
first phenyl ring), 7.56 (d, 4H, second phenyl ring), 7.61, 7.83 (s, 2H, third
phenyl ring).
ꢀ
1
Comp.3C : IR (KBr): vmax/cm
3071 (-C-H str.), 1660 (-C ¼ O, group), 1610
8
(
-C ¼ C-) aromatic, 1720 (-COO- group), 1463 (-NO str.), 1240 (-O-CH - ether link-
2
2
1
age), 618 (polymethylene group of –OC H ), 961 (trans, alkene). HNMR: 0.88-0.90 (t,
8
17
6
H, -CH of disubstituted –OC H and –OC H group), 1.46 (q, 6H, -disubstituted
3 4 9 8 17
–
OC H and –OC H group), 1.74 (p, 6H, -disubstituted –OC H9 and –OC H
4 9 8 17 4 8 17
group), 1.28-1.30 (m, 8H, –OC H17 group), 4.06 (t, 6H, -disubstituted –OC H and
8
4
9
–
OC H group), 7.83 (d, J ¼ 15.4 Hz, -CO-CH ¼ CH-), 8.14 (d, J ¼ 15.4 Hz, -CO-
8
17
CH ¼ CH-), 7.11 (d, 4H, first phenyl ring), 7.56 (d, 4H, second phenyl ring), 7.62, 7.82
s, 2H, third phenyl ring).
(
3. Result and discussion
The mesomorphic behaviour of the present compounds was analysed by using polariz-
ing optical microscope (POM), differential scanning calorimetry (DSC), and high tem-
perature X-ray diffraction (XRD).
3.1. Synthesis and characterisation
In order to study the influences of the different numbers of mesogens on mesomorphic
properties, k-shaped two linking group based LCs (13 compounds, series-1) and (5
compounds, series-2) were designed as target compounds. The synthetic route for the
preparation of the target molecules is represented in scheme 1 and scheme 2. The
synthesis of 4-n-alkoxy benzoic acid (1c) is synthesized by refluxing the various alkyl
bromides (R-Br) in methanol [32]. 3,4-dibutoxy benzaldehyde (2a) and 3,4-dibutoxy
5-nitro benzaldehyde (3a) were prepared by refluxing the reaction mixture with butoxy
bromide (C H Br), anhydrous K CO in dry acetone [33]. The (E)-3-(3,4-dibutoxy-
4
9
2
3
phenyl)-1-(4-hydroxy phenyl) prop-2-en-1-one (2b) is prepared by treating of
-hydroxy acetophenone and 3,4-dibutoxy benzaldehyde (2a) in ethanol [34]. Similarly,
E)-3-(3,4-dibutoxy-5-nitrophenyl)-1-(4-hydroxy phenyl) prop-2-en (3b) is prepared by
4
(
treating of 4-hydroxy acetophenone and 3,4-dibutoxy 5-nitro benzaldehyde (3a) in etha-
1
nol [34]. The H NMR of comp.2b shows doublet of 2H at (d ¼ 7.52 ppm and
ꢀ
1
d ¼ 8.04 ppm). From FT-IR, the peak found at 1630 cm
signifying the presence
1
of > C¼O group. The H NMR of comp.3b shows doublet of 2H at (d ¼ 7.52 ppm and
d ¼ 8.04 ppm). From FT-IR, the peak found at 1660 cmꢀ signifying the presence
1

1
06
V. S. SHARMA ET AL.
Scheme 1. Synthesis of chalcone-ester based k-shaped LCs (series-1).
Reagents and conditions: (a) MeOH, conc.H SO , Reflux; (b) R-Br, KOH, dry Acetone, Reflux; (c) KOH,
2
4
EtOH, Reflux; (d) C H Br, Anhy.K CO , dry Acetone, Reflux; (e) 4-hydroxy acetophenone, KOH, ETOH,
4
9
2
3
stirring at RT; (f) DCC, DMAP, DCM, 24 hr. stirring at RT.
of > C¼O group. The final target compounds of series-1 and series-2 were prepared by
modified method using DCC and DMAP in dichloromethane for 48 hr to get the final
compounds of series [35]. The resultant crude residue was purified by using column
chromatography on silica gel eluting with ethyl acetate: hexane as eluent (3:2). FT-IR
ꢀ
1
ꢀ1
results shows peak at 1740 cm for ester group and 1660 cm for ketone group. The
1
H NMR results also well supported to the corresponding structures of comp.2C , 2C ,
1
10
2
C , 3C , 3C are mention n ESI.
16 1 12
3
.2. DSC analysis
DSC is a valuable method for the detection of phase transitions. The thermal behaviour
of present synthesized compounds was confirmed by using DSC measurement depicted
in Fig. 1. In present study, DSC thermogram is traces in heating and cooling condition.
An examination of crystal to mesophase transition temperatures reveal that with
increasing alkyl chain length in left tail group, a decrease in transition temperatures.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
107
Scheme 2. Synthesis of chalcone-ester based k-shaped LCs (series-2).
Reagents and conditions: (g) C H Br, Anhy.K CO , dry Acetone, Reflux, 4 hr; (h) 4-hydroxy acetophe-
4
9
2
3
none, KOH, ETOH, stirring at RT; (i) DCC, DMAP, DCM, 24 hr. stirring at RT.
ꢁ
Comp.2C10 shows three endothermic peaks at 93.8 C, 102.1˚C and 118.6˚C on heating
trace, which is corresponded to crystal to SmC, SmC to nematic and nematic to iso-
tropic phase transition. While on cooling cycles, these endothermic peaks observed at
ꢁ
9
9
2.7˚C and 111.8˚C. Comp.2C18 exhibits endothermic peaks at 65.2 C, 76.7˚C and
7.3˚C corresponding to the presence of three transition which is reappear on cooling
cycles and also confirmed by POM study. Comp.2C12 shows first endothermic peaks at
1.3˚C for crystal to SmC phase, second endothermic peak exhibit at 102.5˚C for SmC
9
to nematic transition while the third endothermic peak observed at 115.6˚C that corres-
pondence to nematic to isotropic phase. These cycles again reappear on cooling condi-
tion. Comp.3C shows endothermic peaks at 75.6˚C, 85.6˚C and 95.1˚C on heating
4
conditions and on cooling conditions it again traces at 92.8˚C and 103.7˚C to confirm
the presence of three phase transition which is further confirmed by POM study. The
DSC measurement of comp.3C and 3C is shown in Fig. 2. Compound 3C traces
8
18
8
three endothermic peaks at 71.5˚C, 82.5˚C and 92.6˚C on heating condition which is
correspondences to crystal to SmC, SmC to nematic and nematic to isotropic phase
transition and on cooling condition, it again traces at 70.9˚C and 83.1˚C. Comp. 3C18
exhibits only two endothermic peaks on heating condition at 65.9˚C and 79.9˚C to con-
firm the presence of crystal to nematic and nematic to isotropic phase transition.
Transition temperature obtained by DSC analysis at heating condition and the value of
enthalpy and entropy are listed in Table 1.
3
.3. POM investigation
The transition temperatures of newly synthesized compounds of series-1 & series-2
were carried out on the basis of the polarizing optical microscope (POM) by observing
the textures when sample was sandwiched between a glass slide and a cover slip is

1
08
V. S. SHARMA ET AL.
Figure 1. The DSC traces of compounds (a) 2C10 (series-1); (b) 2C18 (series-1); (c) 2C12 (series-1); (d)
C4 (series-2).
3
mention in Table 1. All the synthesized compounds show enantiotropic mesophase with
good thermal stability. In series-1, lower members (2C to 2C ) do not display any mes-
1
3
ophase and directly transform into isotropic liquid from crystal phase due to presence
of short alkyl spacer on left alkoxy side chain. Comp.2C to 2C exhibits only nematic
4
8
mesophase without presence of any smectic phases while higher members (2C10 to
C ) shows smectic C as well as nematic mesophase, this is mainly attributed due to
2
1
8
the presence of long alkyl spacer at left side chain to form lamellar order type layered
structure. In second series, comp.3C shows non-liquid crystalline behaviour while
1
comp.3C , 3C shows enantiotropical smectic C and nematic phase. The higher mem-
4
8
bers of comp.3C ,3C shows only nematic mesophase. The thermal behaviour of ser-
1
2
18
ies-1 and series-2 is shown in Fig. 3 and Fig. 4.
3
.3.1 Textural study
The optical texture image of series-1 & series-2 are shown in Fig. 5 and Fig. 6. The
presence of mesomorphism in both series-1 & series-2 are enantiotropical in nature.
The texture patterns of smectic C phase are broken fan and gradian shape type while
the texture images of nematic phase are threaded and schlieren type in both series.
Comp.2C , on heating at 91˚C, it shows broken fan type texture pattern of SmC phase.
1
2
Comp. 2C exhibited schlieren type texture image of nematic phase at 112˚C on heating
7

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
109
Figure 2. The DSC traces of compounds (a) 3C (series-1); (b) 3C18 (series-2).
8
ꢁ
ꢀ1
ꢀ1 ꢀ1
Table 1. Phase transition temperature ( C) and enthalpy (J g ) and entropy change (J g
k
) by DSC
measurement.
ꢁ
ꢁ
-1
-1
-1 -1
-1 -1
Comp.
Transition
Heating scan ( C)
Cooling scan ( C)
DH (Jg )
DH (Jg )
DS (J g k )
DS (J g k )
2C
2C
2C
3C
3C
3C
10
18
12
4
Cr-SmC
SmC-N
N-I
Cr-SmC
SmC-N
N-I
Cr-SmC
SmC-N
N-I
Cr-SmC
SmC-N
N-I
Cr-SmC
SmC-N
N-I
Cr-N
N-I
93.8
102.1
118.6
65.2
76.7
97.3
91.3
102.5
115.7
75.6
85.6
95.1
71.5
82.5
92.6
65.9
79.9
92.1
108.7
111.9
67.6
80.1
94.1
3.54
7.85
9.12
8.10
12.74
6.34
1.64
8.02
4.98
6.36
10.01
11.74
7.53
12.96
6.23
7.65
11.43
1.69
6.53
12.05
2.45
9.43
9.81
5.32
1.42
7.31
4.62
12.41
9.78
5.67
11.76
5.58
5.61
9.54
0.0096
0.0209
0.0232
0.0239
0.0364
0.0171
0.0045
0.0213
0.0128
0.0182
0.0279
0.0318
0.0218
0.0364
0.0170
0.0225
0.0323
0.0046
0.0171
0.0313
0.0071
0.0267
0.0267
0.0146
0.0036
0.0018
0.0133
0.0339
0.0259
0.0164
0.0330
0.0151
0.0166
0.0271
90.6
108.9
117.4
72.5
92.8
103.7
70.9
83.1
98.4
64.2
78.7
8
18
condition. Comp.2C16 displayed gradian type texture image at 79˚C on heating condi-
tion. Comp.2C18 displayed schlieren type texture pattern of nematic phase at 79˚C on
cooling condition. Furthermore, comp.3C displayed broken fan type texture image of
8
SmC phase at 71˚C on heating condition. Comp.3C12 exhibited schlieren type texture
image of nematic phase at 68˚C on cooling condition. The phase transition temperature
of present synthesized series is mention in Table 2.
3
.3.2 Comparative Study
Some LC properties evaluated from thermotropic data of presently investigated newly
series-1 with compared with series-2 as shown in Fig. 7. Both the series-1 and series-2
are same with respect to two linkage group and terminally fixed disubstituted butoxy
side group with variable side chain on left alkoxy part. The linearity of both the series
are same but the breadth of series-2 is higher as compare to series-1 due to presence of
-
nitro group substituted at lateral side on second phenyl unit. The temperature range of
mesophase in series-1 is higher as compare to series-2, this is observed due to the

1
10
V. S. SHARMA ET AL.
Figure 3. Bargraph summarizing the thermal behavior of comp. 2C -2C (Series-1) (heating cycle).
1
18
Figure 4. Bargraph summarizing the thermal behavior of comp. 3C -3C (Series-2) (heating cycle).
1
18
presence of nitro group which increasing the polarity and polarizability of molecules
and decrease the transition temperature as compare to series-1. Thus, changing in LC
properties like thermal stability and temperature range, commencement of mesophase
etc. will be influenced by the magnitudes of changing features of homologous series-1
and series-2 taken under comparative study. Thermal stability of SmC and nematic
phase of series-1 is 94.6˚C and 119.3˚C while for series-2, it is exhibited at 82.5˚C and
82.2˚C which is lower as compare to series-1.
3
.4. Chemical reactivity
The calculated FMO distributions of comp.2C , 3C , 2C and 3C12 are shown in Fig. 8
1
1
12
to Fig. 11. From Fig. 8, the HOMO is localized on the di-butoxy group substituted
group on third phenyl ring while the LUMO is mostly concentrated on chalconyl group
and slightly localized on third phenyl ring. In comp.3C , the HOMO is mostly concen-
1
trated on di-butoxy group and slightly on chalcone group while the LUMO is localized
on chalcone group with third phenyl ring. In comp.2C12, the HOMO is localized on

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
111
Figure 5. Photomicrographs of the texture obtained for series-1: (a) broken fan type texture image of
SmC phase at 91˚C for comp. 2C ; (b) schlieren type texture image of nematic phase at 112˚C for
12
comp. 2C ; (c) gradian type texture image of SmC phase at 79˚C for comp. 2C ; (d) schlieren type
7
16
texture image of nematic phase at 79˚C for comp. 2C .
1
8
Figure 6. Photomicrographs of the texture obtained for series-1: (a) broken fan type texture image of
SmC phase at 71˚C for comp. 3C ; (b) schlieren type texture image of nematic phase at 68˚C for
8
comp. 3C .
1
2
di-butoxy group while the LUMO is localized slightly on chalcone core. Presence of
nitro group and left alkyl side chain in 3C12 affects its electronic properties. The
HOMO is localized on chalcone group while the LUMO is localized slightly on di-
butoxy side group. Presence of nitro group on lateral side shows significant influence
on the HOMO and LUMO orbitals. The HOMO-LUMO gap of comp.3C , 3C (series-
1
12

1
12
V. S. SHARMA ET AL.
ꢁ
Table 2. Transition Temperature in C by POM.
ꢁ
Transition temperatures in C
Sr no
R ¼ n-alkyl group
Cr-I
Cr-SmC
Cr/SmC-N
N-I
1
2
3
4
5
6
7
8
9
2C
2C
2C
2C
2C
2C
2C
2C
1
2
3
4
5
6
7
8
158.0
152.0
147.0
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
ꢂ
–
–
–
–
–
–
ꢂ
–
–
–
–
–
–
ꢂ
ꢂ
121.0
118.0
114.0
112.0
107.0
104.0
101.0
98.0
91.0
79.0
–
143.0
139.0
132.0
129.0
121.0
114.0
112.0
108.0
101.0
94.0
–
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
2C10
2C12
2C14
2C16
2C18
ꢂ
94.0
91.0
82.0
79.0
62.0
–
79.0
71.0
–
ꢂ
ꢂ
10
11
12
13
14
15
16
17
18
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
3C
3C
3C
1
4
8
112.0
–
ꢂ
–
ꢂ
–
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
84.0
81.0
68.0
64.0
93.0
84.0
79.0
73.0
ꢂ
ꢂ
ꢂ
3C12
3C18
–
–
ꢂ
ꢂ
–
ꢂ
ꢂ
(
Cr ¼ Solid Crystal, SmC ¼ Smectic C phase, Nm ¼ Nematic phase, Iso ¼ Isotropic phase).
Figure 7. Ball-stick model of (a) series-1; (b) series-2.
2
) is lower as compare to comp.2C 2C (series-1). Hence, smaller the HOMO-LUMO
1, 12
gaps correspond to better stability and reactivity. Thus, nitro substituted compounds of
series-2 is most stable as compare to series-1. It can be noted that the electronic proper-
ties of comp.2C , 3C and 2C , 3C could have originated from the chalconyl-phenyl
1
1
12
12
unit substituted by di-butoxy side group at tail and lateral side interaction. The energy
difference between the HOMO and LUMO is termed as HOMO-LUMO gap. The
HOMO-LUMO gap of some compounds from both the series is shown in Table 3. The

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
113
Figure 8. The molecular orbitals and energy for the HOMO and LUMO of comp.2C (series-1)
1
.
Figure 9. The molecular orbitals and energy for the HOMO and LUMO of comp.3C (series-2)
1
.
8
Table 3. HOMO-LUMO energy value of comp.C (series-1, series-2).
Comp. HOMO
LUMO
Energy gap
2C
3C
2C
3C
1
(series-1)
(series-2)
12 (series-1)
12 (series-2)
ꢀ10.368 eV
ꢀ9.893 eV
ꢀ10.954 eV
ꢀ9.892 eV
ꢀ6.186 eV
ꢀ6.151 eV
ꢀ6.165 eV
ꢀ6.151 eV
4.182 eV
3.742 eV
4.322 eV
3.741 eV
1
presence of nitro group at lateral side effects the possibility of charge transfer of electron
in the HOMO to the LUMO. The higher value of HOMO energy contributes negatively
to the activity due to presence of di-butoxy and left side group as electron-donating
group which increase the energy of the HOMO orbitals.

1
14
V. S. SHARMA ET AL.
Figure 10. The molecular orbitals and energy for the HOMO and LUMO of comp.2C (series-1)
.
1
2
Figure 11. The molecular orbitals and energy for the HOMO and LUMO of comp.3C (series-2)
.
1
2
3.5. XRD analysis
The mesophase structures of novel chalconyl-ester LCs were further confirmed by X-ray
diffraction (XRD) studies of comp.2C , comp.2C and comp.3C filled in Lindemann
1
0
12
8
capillaries. The X-ray patterns of LC phases of compounds 2C , 2C and 3C showed
10
12
8
sharp intense peak in small angle region and single diffuse scattering peak in the wide
angle region are shown in Fig. 12 to Fig. 14. The XRD pattern obtained for comp.2C10
at 94.0˚C and 104.0˚C corresponding to smectic C and nematic phase is mention in
Fig. 12. The sharp reflection in the small angle region with d-spacing is 14.924 Å of
comp.2C10 which is slightly smaller than the molecular length 16.853 Å indicating the
tilted organization of the molecules in the layers and a d-spacing of the diffuse peak at
high-angle region is 4.10 Å. The presence of sharp reflection in the small angle region

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
115
Figure 12. XRD patterns of compound 3C10 (series-1) at 94˚C and 104˚C.
Figure 13. XRD patterns of compound 3C12 (series-1) at 91˚C and 101˚C.
is characteristic of layer ordering of smectic C phase and for the nematic mesophase
without any positional order arrangement in the molecules. The diffractograms for
comp.2C12 shows one diffuse reflection in the small–angle region and a diffuse peak at
wide-angle region. The d-spacing of comp.2C12 are 15.231 Å, and 4.02 Å. The d-spacing
of comp.3C are 14.231 Å, and 4.29Å which are due to the presence of lamellar order-
8
ing. From the microscopic observations with this reflection patterns confirm the type of
the phase is SmC. The proposed mechanism of the arrangement of molecules in SmC
and nematic phase present in series-1 and series-2 are shown in Fig. 15 and Fig. 16.
Both the series shows LCs phase on heating as well as cooling condition respectively.
The presence of smectic mesophase in presence both series are more ordered than the
nematic phase.
4. Conclusions
In summary, we have synthesized k-shape three-ring based LCs having chalconyl-ester
linking unit with variable side chain at left end and fixed di-substituted butoxy group at

1
16
V. S. SHARMA ET AL.
Figure 14. XRD patterns of compound 3C (series-2) at 79˚C and 84˚C.
8
Figure 15. Proposed mechanism of present series-1.
terminal side. Both the series are differing at lateral side group with respect to each
other. A significant change in the mesophase range, structure and properties are
observed upon addition of nitro group at lateral side in series-2 which increases the
polarity and polarizability of molecules. The existence of polar nitro group at lateral
side significantly increases the dipole moment which can induce the polar switching in
the mesophase of the compounds. In series-1, smaller terminal alkyl chain compounds
display nematic mesophase and a longer alkyl chain compound favors the SmC phase
and nematic mesophase. In series-2, comp.3C and 3C shows SmC and nematic phase
4
8
while higher member shows only nematic phase. The POM and DSC measurements
confirmed the presence of enantiotropic nematic as well as SmC mesophase. The group
efficiency order derived on the basis of (a) thermal stability, (b) early or late commence-
ment of mesophase, (c) Temperature range of mesophase.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
117
Figure 16. Proposed mechanism of present series-2.
Acknowledgment
Authors acknowledge thanks to Department of Basic and Applied Sciences, Madhav University
for providing lab facility. Authors are also thankful to NFDD Centre for providing analytical and
spectral services.
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