New chalcone based liquid crystals with allylidene amino linking unit: Synthesis and characterization

Article abstract of DOI:10.1080/15421406.2018.1499697

In this study, the synthesis, structural characterization and mesomorphic properties of newly thirteen calamitic shaped compounds derived from allylidene amino chalcone and 4-n-alkoxy benzoyloxy benzoic acid. Comp.H₁ to H₃ exhibited nonliquid crystalline nature, while comp.H₄ to comp.H₁₈ displayed enantiotropical smectic C phase. Phase transition temperatures of present synthesised compounds were determined by optical polarising microscopy (POM), differential scanning calorimetric (DSC) and powder X-ray diffraction (PXRD) techniques. Thermal stabilities of smectic to isotropic phase are 150.0 °C and temperature range of mesophase is in decreasing order from comp.H₃ to comp.H₁₈ respectively. The presences of SmC phase are the type of broken fan and needle type in present synthesized series. It is also shown that presence of chalcone amino allylidene central linking group favors a calamitic liquid crystalline behaviour in molecules with lower member to higher member aliphatic side chain in alkoxy group (-OR).

Full text of DOI:10.1080/15421406.2018.1499697

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: https://www.tandfonline.com/loi/gmcl20
New chalcone based liquid crystals with allylidene
amino linking unit: Synthesis and characterization
Vinay S. Sharma, Anuj S. Sharma, Upendra H. Jadeja & Deepak Suthar
To cite this article: Vinay S. Sharma, Anuj S. Sharma, Upendra H. Jadeja & Deepak
Suthar (2018) New chalcone based liquid crystals with allylidene amino linking unit:
Synthesis and characterization, Molecular Crystals and Liquid Crystals, 665:1, 64-81, DOI:
10.1080/15421406.2018.1499697
To link to this article: https://doi.org/10.1080/15421406.2018.1499697
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MOLECULAR CRYSTALS AND LIQUID CRYSTALS
2018, VOL. 665, NO. 1, 64–81
https://doi.org/10.1080/15421406.2018.1499697
New chalcone based liquid crystals with allylidene amino
linking unit: Synthesis and characterization
Vinay S. Sharmaa, Anuj S. Sharmab, Upendra H. Jadejac, and Deepak Suthard
aDepartment of Chemistry, Faculty of Basic and Applied Science, Madhav University, Sirohi, Rajasthan,
b
India; Department of Chemistry, School of Science, Gujarat University, Ahmedabad, Gujarat, India;
d
cPresident Science College, Gujarat University, Ahmedabad, Gujarat, India; Department of Physics,
Faculty of Basic and Applied Science, Madhav University, Sirohi, India
KEY WORDS
ABSTRACT
Allylidene amino; chalcone;
mesophase; smectic C
In this study, the synthesis, structural characterization and mesomorphic
properties of newly thirteen calamitic shaped compounds derived from
allylidene amino chalcone and 4-n-alkoxy benzoyloxy benzoic acid.
Comp.H1 to H3 exhibited nonliquid crystalline nature, while comp.H4 to
comp.H18 displayed enantiotropical smectic C phase. Phase transition
temperatures of present synthesised compounds were determined by
optical polarising microscopy (POM), differential scanning calorimetric
(DSC) and powder X-ray diffraction (PXRD) techniques. Thermal stabilities
of smectic to isotropic phase are 150.0 ꢀC and temperature range of mes-
ophase is in decreasing order from comp.H3 to comp.H18 respectively.
The presences of SmC phase are the type of broken fan and needle type
in present synthesized series. It is also shown that presence of chalcone
amino allylidene central linking group favors a calamitic liquid crystalline
behaviour in molecules with lower member to higher member aliphatic
side chain in alkoxy group (-OR).
GRAPHICAL ABSTRACT
1. Introduction
The arrangement of molecules in liquid crystals (LCs) takes place in a number of ways
leading to various phases of different order and symmetry between crystalline solid and
CONTACT Vinay S. Sharma
vinaysharma3836@gmail.com
Department of Chemistry, Faculty of Basic and Applied
Science, Madhav University, Sirohi, Rajasthan, India.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gmcl.
ß 2018 Taylor & Francis Group, LLC

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
65
isotropic liquid [1–4]. Calamitic molecules of conventional and unconventional liquid
crystalline materials have been intensively investigated for scientific and technological
potent applications such as sensing materials, optoelectronic display materials and bio-
logically active molecules [5–6]. Study on LC state is planned with a view to understand
and establish the effect of molecular structure on LC properties [7] as a consequence of
molecular rigidity and flexibility by using different linking group [8]. Molecules incor-
porated with two or more than two linking group have attracted a great attention from
the researchers in designing a new calamitic rod shaped liquid crystalline materials [9].
Literature studies revealed that the chalcone has been widely employed as a linking
group for the synthesis of calamitic liquid crystals [10–11]. Chalcones with presence of
electron-pulling and electron-pushing functional groups on the benzene rings leads
calamitic shaped of molecules [12–14]. Several kinds of chalcone monomer, dimer and
polymeric compounds of different shapes have been evaluated for their materials prop-
erties. Tandel et al. synthesized polymer chalcone exhibited nematic phase [15]. 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 [16–19]. Yeap et al. have also synthesized mesomorphic com-
pounds containing on ester-chalcone linkage [20]. Recently, Gallardo and his coworkers
reported polycatenar liquid crystals series based on bent shaped chalcone and cyanopyr-
idine molecules [21]. Patel et al. reported rod type homologous series having chalconyl
ester central linkage group and hexyloxy tail group [22]. 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 [23]. Previously, Yellamaggad and co-worker have reported the
bent-core unsymmetrical dimers in which cholesteryl ester and chalconyl moiety are
present, which enhances the biaxiality and chirality of the system [24]. Furthermore,
Bhoya et al. reported chalconyl-ester linking group based homologous series [25].
Figure 1 indicates the reported liquid crystal materials based on allylidene amino and
chalcone group in literature [26–27]. Our research group also reported some linear and
nonlinear homologous series which consisted three phenyl rings bonded through vinyl
Figure 1. Different type of LCs material based on allylidene amino-chalcone group.

66
V. S. SHARMA ET AL.
ester (-CH¼CH-COO-) and ester (-COO-) linkage group connected with chalconyl cen-
tral group having alkoxy terminal group at left end and different terminal group or lat-
eral substitution on right side [28–30]. We have also reported the single chalconyl
linkage group between two phenyl rings exhibited monotropy or enantiotropy meso-
phase with low thermal stability [31–33]. In continuation of our efforts to synthesized
newly liquid crystalline materials, we have introduce some new calamatic liquid crystal
based on two ester group (-COO-) with chalcone (-CH¼CH-CO-) and allylidene amino
(-N¼CH-CH¼CH-) group. We have compared the thermal stability and temperature
range of mesophase of series-1 with series-A1 and series-A2 which was previously
reported by our research group. Here in, we present five phenyl ring based calamitic
LCs having four linking units. The aim of this work is to better understand how the
chemical nature of different linking group affect liquid crystalline property, and to
achieve this, we have introduce one more phenyl ring connected through ester group in
present newly synthesized series.
2. Experimental
2.1. General
For the synthesis of target compounds in present newly homologous series, the follow-
ing materials were used: 4-hydroxy benzoic acid, 4-hydroxy benzaldehyde, 4-amino ace-
tophenone were purchased from SRL, (Mumbai), Alkyl halides (R-Br) were purchased
from Lancaster, (England), cinnamaldehyde was purchased from (Sigma Aldrich), DCC
(Dicyclohexyl carbodimide) was purchased from Fluka Chemie (Switzerland), Dimethyl
amino pyridine DMAP (4,40-dimethylamino pyridine) was purchased from Finar chemi-
cals (India), Dichloro methane, Ethanol, MeOH, required for synthesis were used as
received except solvents which was dried and distilled prior to use. The molecular struc-
tures of the target products and the intermediates were confirmed by spectroscopic
techniques. Representative homologous series were characterised by elemental analysis,
Infrared spectroscopy, 1H NMR spectra. IR (cmꢁ1, KBr) spectra were recorded by
1
Perkin-Elmer spectrum GX in the frequency range of 4000-400 cmꢁ1, H NMR spectra
were recorded on Bruker (300 MHz, CDCl3) using tetramethylsilane as an internal
standard. Microanalysis was performed on Perkin-Elmer PE 2400 CHN analyser. The
textural observation was carried out by using a polarising optical microscope equipped
with hot stage along with the temperature controller and camera. Decomposition tem-
peratures were determined using of Shimadzu (DSC) differential Scanning Calorimeter
with a heating rate of 5ꢀC to 10.0 ꢀC minꢁ1
.
2.2. Synthesis of compounds in present series
2.2.1. Synthesis of 4-n-alkoxy benzoic acid (C)
4-n-alkoxy derivatives of 4-hydroxy benzoic acid were prepared by reported method by
Dave and Vora [34].

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
67
2.2.2. Synthesis of Methyl-4-hydroxy benzoate (A)
Equimolar proportion of p-hydroxy benzoic acid and absolute methanol shacked well in
presence 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.126ꢀC, yield 79%) [35].
2.2.3. Synthesis of 4-(Methoxy carbonyl) phenyl 40-n-alkoxy benzoate (D)
4-(methoxy carbonyl) phenyl 40-n-alkoxy benzoate has been prepared by esterification
of the appropriate 4-n-alkoxy benzoic acid (C) (2.02 mmol) and methyl-4-hydroxy
benzoate (A) (2.02 mmol), dicyclohexyl carbodiimide (DCC) (2.22 mmol) and dimethy-
laminopyridine (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 filtration and remove, while the filtrate was evaporated to dry-
ness. The resultant crude residue was purified by column chromatography on silica gel
eluting with methanol: chloroform as eluent (2:4) [36].
Comp. D4: IR (KBr): vmax/cmꢁ1 3033 (C-H str.), 679 polymethylene group of
–OC4H9 chain group, 1740 (-COO- group), 1240 (C-O str.). 1HNMR: 0.88 (t, 3H,
–OC4H9), 1.45 (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%.
2.2.4. Synthesis of 4-((40-n-alkoxy benzoyl) oxy) benzoic acid (E)
4-((40-n-alkoxy benzoyl) oxy) benzoic acid (E) were prepared by dissolving comp.D 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 [37].
Comp. E4: IR (KBr): vmax/cmꢁ1, 3071 (C-H str.), 3301 (-OH of carboxylic group),
1680 (C¼O str. of carboxylic group), 1750 (-COO- group), 648 polymethylene group of
1
–OC4H9 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%.
2.2.5. Synthesis of 1-(4-(((E)-3-phenyl allylidene) amino) phenyl) ethan-1-one (F)
1-(4-(((E)-3-phenyl allylidene) amino) phenyl) ethan-1-one (F) was synthesized by
refluxing the mixture of cinnamaldehyde (2 mmol.) and 4-amino acetophenone
(2 mmol.) in EtOH for 3 hr. in presence of few drops acetic acid as catalyst. The yellow
precipitate is obtained which was further wash with ethanol several times. The obtain

68
V. S. SHARMA ET AL.
residue was further purified by using column chromatography on silica gel eluting with
chloroform: methanol as eluent (4:1) [38]. IR (KBr): vmax/cmꢁ1 3079 (-C-H str.), 1661
(-C¼O group of –COCH3), 1580 (-C¼C-) aromatic, 962 (trans, alkene), 1590
1
(-CH¼N). HNMR: 2.03 (s, 3H, -CH3), 8.41 (s, 1H, -CH¼N), 7.22 (d, J¼15.1 Hz, 1H,
-CH¼CH-CH¼N), 6.83 (d, J¼15.1 Hz, 1H, -CH¼CH-CH¼N), 7.38, 7.54 (d, 5H, first
phenyl ring), 7.33, 8.02 (d, 4H, second phenyl ring). Elemental analysis: calculated for
C17H15ON: C, 81.92; H, 6.02; N, 5.62; found: C, 80.69; H, 5.95; N, 5.54.
2.2.6. Synthesis of (2E)-3-(4-hydroxy phenyl)-1-(4-(((E)-3-phenyl allylidene) amino)
phenyl) prop-2-en-1-one (chalcone) (G)
Chalcone (G) was prepared by usual established method reported in literature [38].
(brownish yellow, Yield: 67%), IR (KBr): vmax/cmꢁ1 3460 (-OH str.-bonded), 3079-3020
(-C-H str. aliphatic alkyl group), 2932, 1598 (CH¼N), 1667 (-C¼O, group), 1584-1610
(-C¼C-) aromatic, 1280 (-O-CH2- ether linkage), 962 (Trans alkene). Elemental ana-
lysis: calculated for C24H19O2N: C, 81.58; H, 5.38; O, 9.06; N, 3.96%; found: C, 81.48;
H, 5.28; O, 8.77; N, 3.89%.
2.2.7. General procedure for the synthesis of final target compounds (H)
The final target compounds (H) has been prepared by esterification of the appropriate
compound (E) (2 mmol) and compound (G) (2 mmol), dicyclohexyl carbodiimide
(DCC) (2.22 mmol) and dimethylaminopyridine (DMAP) in catalytic amount
(0.2 mmol) in dry CH2Cl2 (DCM) (40 ml) was stirred at room temperature for 48 h. The
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 methanol: chloroform as
eluent (1:4) [39]. The characterization data of target compounds mention in supporting
information. The synthesis route of target compounds was mention in below Scheme 1.
Compound H1: IR (KBr): vmax/cmꢁ1 2960 (C-H str. of alkane), 1640 (C¼O str. of
carbonyl carbon of chalconyl group), 1601 (C¼C str. of alkene in chalcone), 1760
(-COO- group), 770 (C-H bending of alkene), 1120 (C-O str. of ether linkage), 1240
1
(C-O str. of carbonyl (>C¼O) group), 960 (trans, -CH¼CH- group). H-NMR: 3.81
(t, 3H, –OCH3), 7.81 & 7.52 (d, 2H, -CH¼CH-CO-), 7.44 (d, 1H, -N¼CH-CH¼C-),
6.83 & 7.20 (d, 2H, -N¼CH-CH¼CH-), 8.07 & 7.10 (d, 4H, Ar), 7.32 & 7.72 (d, 6H,
Ar), 7.87 & 7.38 (d, 6H, Ar), 7.61, 7.40, 7.31 (d, 5H, Ar). Elemental analysis: calculated
for C39H25O6N: C, 77.61%; H, 4.14%; O, 15.92%; N, 2.32%; found: C, 77.25%; H, 4.03%;
O, 15.97%; N, 2.23%.
Compound H2: IR (KBr): vmax/cmꢁ1 2960 (C-H str. of alkane), 1650 (C¼O str. of
carbonyl carbon of chalconyl group), 1610 (C¼C str. of alkene in chalcone), 1730
(-COO- group), 992 (C-H bending of alkene), 1120 (C-O str. of ether linkage), 1240
1
(C-O str. of carbonyl (>C¼O) group, 960 (trans, -CH¼CH- group). H-NMR: 1.32 (t,
3H, –OC2H5), 4.06 (t, 2H, –OC2H5), 7.82 & 7.52 (d, 2H, -CH¼CH-CO-), 7.46 (d, 1H,
-N¼CH-CH¼CH-), 6.83 & 7.21 (d, 2H, -N¼CH-CH¼CH-), 8.07 & 7.10 (d, 4H,Ar),
7.32 & 7.71 (d, 6H, Ar), 7.87 & 7.38 (d, 6H, Ar), 7.61, 7.40, 7.32 (d,5H, Ar). Elemental

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
69
Scheme 1. (i) MeOH, conc.H2SO4, Reflux, 30 min; (ii) R-Br, KOH, MeOH, Reflux; (iii) KOH, EtOH, Reflux;
(iv) DCC, DMAP, DCM, 24 hr. rt stirring; (v) EtOH, few drops of acetic acid, Reflux; (vi) KOH, EtOH, rt
stirring; (vii) DCC, DMAP, DCM, 48 hr. rt stirring.

70
V. S. SHARMA ET AL.
analysis: calculated for C40H27O6N: C, 77.79%; H, 4.37%; O, 15.55%; N, 2.26%; found:
C, 77.48%; H, 4.29%; O, 15.48%; N, 2.23%.
Compound H3: IR (KBr): vmax/cmꢁ1 2950 (C-H str. of alkane), 810 (–(CH2-)n group
of –OC3H7 chain), 1650 (C¼O str. of carbonyl carbon of chalconyl group), 1610 (C¼C
str. of alkene in chalcone), 1750 (-COO- group), 1420 (-C¼C str. of aromatic ring), 984
(C-H bending of alkene), 1188 (C-O str. of ether linkage), 1240 (C-O str. of carbonyl
1
(>C¼O) group, 962 (trans, -CH¼CH- group). H-NMR: 0.92 (t, 3H, –OC3H7), 1.76 (p,
2H, -OC3H7), 4.06 (t, 2H, –OC3H7), 7.87 & 7.51 (d, 2H, -CH¼CH-CO-), 7.48 (d, 1H,
-N¼CH-CH¼C-), 6.84 & 7.22 (d, 2H, -N¼CH-CH¼CH-), 8.06 & 7.12 (d, 4H, Ar), 7.30
& 7.72 (d, 6H, Ar), 7.86 & 7.38 (d, 6H, Ar), 7.61, 7.40, 7.31 (d, 5H, Ar). Elemental ana-
lysis: calculated for C41H29O6N: C, 77.97%; H, 4.59%; O, 15.21%; N, 2.21%; found: C,
77.91%; H, 4.48%; O, 15.17%; N, 2.15%.
Compound H4: IR (KBr): vmax/cmꢁ1 2940 (C-H str. of alkane), 1640 (C¼O str. of
carbonyl carbon of chalconyl group), 1601 (C¼C str. of alkene in chalcone), 1760
(-COO- group), 1440 (-C¼C str. of aromatic ring), 994 (C-H bending of alkene), 1188
(C-O str. of ether linkage), 1246 (C-O str. of carbonyl (>C¼O group), 960 (trans,
-CH¼CH- group), 740 polymethylene (-CH2-) of –OC4H9. 1H-NMR: 0.90 (t, 3H,
–OC4H9), 1.76 (p, 2H, -OC4H9), 4.06 (t, 2H, –OC4H9), 7.88 & 7.52 (d, 2H, -CH¼CH-
CO-), 7.48 (d, 1H, -N¼CH-CH¼C-), 6.84 & 7.22 (d, 2H, -N¼CH-CH¼CH-), 8.08 &
7.10 (d, 4H, Ar), 7.31 & 7.74 (d, 6H, Ar), 7.87 & 7.38 (d, 6H, Ar), 7.61, 7.40, 7.32 (d,
5H, Ar). Elemental analysis: calculated for C42H31O6N: C, 78.13%; H, 4.80%; O, 14.88%;
N, 2.17%; found: C, 78.09%; H, 4.73%; O, 14.83%; N, 2.09%.
Compound H8: IR (KBr): vmax/cmꢁ1 2950 (C-H str. of alkane), 1610 (C¼O str. of
carbonyl carbon of chalconyl group), 1610 (C¼C str. of alkene in chalcone), 1740
(-COO- group), 1440 (-C¼C str. of aromatic ring), 991 (C-H bending of alkene), 1180
(C-O str. of ether linkage), 1240 (C-O str. of carbonyl (>C¼O group), 960 (trans,
-CH¼CH- group), 632 polymethylene (-CH2-) of –OC8H17. 1H-NMR: 0.90 (t, 3H,
–OC8H17), 1.76 (p, 2H, -OC8H17), 1.46 (sext, 2H, -OC8H17), 1.28-1.32 (m, 8H,
-OC8H17), 4.06 (t, 2H,–OC8H17), 7.88 & 7.52 (d, 2H, -CH¼CH-CO-), 7.48 (d, 1H,
-N¼CH-CH¼C-), 6.84 & 7.22 (d, 2H, -N¼CH-CH¼CH-), 8.08 & 7.10 (d, 4H, Ar), 7.31
& 7.74 (d, 6H, Ar), 7.87 & 7.38 (d, 6H, Ar), 7.61, 7.40, 7.32 (d, 5H, Ar). Elemental ana-
lysis: calculated for C46H39O6N: C, 78.74%; H, 5.56%; O, 13.69%; N, 1.99%; found: C,
78.71%; H, 5.48%; O, 13.63%; N, 1.93%.
Compound H10: IR (KBr): vmax/cmꢁ1 2950 (C-H str. of alkane), 1640 (C¼O str. of
carbonyl carbon of chalconyl group), 1760 (-COO- group), 1440 (-C¼C str. of aromatic
ring), 991 (C-H bending of alkene), 1188 (C-O str. of ether linkage), 1246 (C-O str. of
carbonyl (>C¼O group), 960 (trans, -CH¼CH- group), 681 polymethylene (-CH2-) of
1
–OC10H21 group. H-NMR: 0.90 (t, 3H, -CH3 of polymethylene –OC10H21), 1.28-1.32
(m, 12H, -OC10H21), 1.76 (p, 2H, -OC8H17), 1.46 (sext, 2H, -OC8H17), 4.06 (t, 2H,
–OC10H21), 7.88 & 7.52 (d, 2H, -CH¼CH-CO-), 7.48 (d, 1H, -N¼CH-CH¼C-), 6.84 &
7.22 (d, 2H, -N¼CH-CH¼CH-), 8.08 & 7.10 (d, 4H, Ar), 7.31 & 7.74 (d, 6H, Ar), 7.87
& 7.38 (d, 6H, Ar), 7.61, 7.40, 7.32 (d, 5H, Ar). Elemental analysis: calculated for
C48H43O6N: C, 79.01%; H, 5.89%; O, 13.16%; N, 1.92%; found: C, 78.94%; H, 5.84%; O,
13.12%; N, 1.89%.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
71
3. Result and discussions
3.1. Mesomorphic behaviour study
Here in present investigation, we have synthesized novel liquid crystalline compounds
having four linking group joint via five phenyl ring in present series-1 from small alkyl
chain (H1) to higher alkyl chain (H18) at left end side group. In present work, we have
study the effect of variation in tail group on mesomorphic property of presently synthe-
sized homologous series. A newly ester-chalcone-allylidene amino linking group based
homologous series (H) synthesised from condensation of 4-((40-n-alkoxy benzoyl) oxy)
benzoic acid (E) and (2E)-3-(4-hydroxy phenyl)-1-(4-((E)-3-phenyl allylidene) amino)
phenyl) prop-2-en-1-one (G) (chalcone) is synthesized and evaluated their LC behaviour
with some thermometric data to compare mesomorphic behaviours and the molecular
structure through molecular rigidity and flexibility with structurally similar previously
reported series by our group. The thermotropic mesophase behaviour of all newly syn-
thesised compounds was primarily investigated by polarising optical microscope (POM).
The exact temperature of phase transition and associated enthalpy values were deter-
mined by differential scanning calorimetry (DSC) analysis. The presence of SmC phase
is confirmed by XRD technique at transition temperature. We have totally prepared
thirteen compounds in present series from lower member to higher member, out of
thirteen compounds, ten compounds (H4 to H18) shows enantiotropic SmC phase with
wide temperature range.
3.1.1. POM study
We have studied the effect of changing aliphatic alkyl chain length in alkoxy (-OR)
group to form calamatic rod type shaped chalcone mesogens. Here, in present article,
we have synthesized five phenyl ring based calamatic rod-shaped homologous series
having two ester (-COO-), chalcone (-CH¼CH-CO-) in presence of allylidene amino
(-N¼CH-CH¼CH-) linking group with no any terminal substituent on right terminal
end. The transition temperature of present series-1 is listed in Table 1. As seen in
Table 1, compounds H1 to H3 shows non LCs property, however comp. H4 to H18 display
Table 1. Transition Temperature in ꢀC by POM (Series-1).
Transition temperatures in ꢀC
Sr.no
R ¼ n-alkyl group
Cr-I
Cr-SmC
SmC-N
SmC-I
1
2
3
4
5
6
7
8
H1
218.0
201.0
198.0
–
–
–
–
–
–
ꢂ
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
H2
H3
H4
H5
H6
H7
H8
H10
H12
H14
H16
H18
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
157.0
146.0
141.0
128.0
139.0
125.0
123.0
118.0
112.0
104.0
191.0
180.0
161.0
142.0
152.0
140.0
138.0
136.0
132.0
128.0
ꢂ
ꢂ
ꢂ
ꢂ
9
ꢂ
10
11
12
13
ꢂ
ꢂ
ꢂ
ꢂ
(Cr-I ¼ Crystal to isotropic phase; Cr-SmC ¼ crystal to smectic C phase; SmC-I ¼ Smectic C to isotropic phase).

72
V. S. SHARMA ET AL.
Figure 2. Phase diagram of series-1.
smectic C phase on heating and cooling condition which was further confirmed by DSC
analysis. Mesophase formation was found to be dependent on the number, position and
the molecular length of the side alkyl chain which increases the flexibility of molecules
attached to the alkoxy side group (-OR). As shown in Table 1, compound H4 has higher
melting type temperature (191ꢀC) and high temperature range of solid crystal to SmC
phase (138.0ꢀC) as compared to higher members of compounds in present series-1.
The phase diagram of present series-1 is shown in Fig. 2 which indicates the phase
behaviour of Cr-SmC/I and SmC-I transition curve present in prepared series-1. It can
be seen that, as series increases from lower homologue H4 to higher homologue H18,
the transition temperature is decreases from upper to lower members of prepared ser-
ies-1. Cr-SmC/I phase transition curve exhibit a smooth falling tendency from H1
homologue to H7 homologue and formerly increases at H8 homologue then continued
to descend upto last homologue H18. Odd-even effect is present at (H7-H8) homologue
in Cr-SmC/I and SmC-I phase transition curve. In addition of decreasing tendency
from H4 to H18 homologous in SmC-I transition curve except H8 homologue, this is
due to the presence of odd-even parity of carbon present in methylene group in side
alkoxy (-OR) group. The decreasing tendency in melting and clearing temperature could
be due to the lowering the vander waals interactions between aromatic phenyl cores
and higher degree of flexibility due to presence of long alkyl chain in alkoxy group at
left terminal part [40]. Comp.H1 to H3 shows non liquid crystalline property due to
presence of short alkyl spacer chain group and high crystallising tendency to directly
transform isotropic liquid without showing any LCs phase.
3.1.2. Textural study
The crystalline compounds placed on clear glass slide sheltered by coverslip were heated
to the isotropic state and heating and cooling rate (2 ꢀC/min) respectively and observing
mesophase texture image. Microphotographs of the textures observed for compounds
H14 and H12 are depicted in Fig. 3. Comp.H8 shows fan like texture image of SmC

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
73
Figure 3. Microphotograph texture image (a) comp.H8 at 139.0ꢀC on heating.
Figure 4. Structurally similar analogous series.
phase at 139.0ꢀC on heating condition and again reappear on cooling condition. Comp.
H14 shows needle type texture image of SmC phase at 118.0ꢀC on cooling condition. It
can be noted that, presence of mesophase in present series is enantiotropical type, con-
dition; (b) comp.H14 at 118.0ꢀC on cooling condition.
3.1.3. Comparative study
Some LC properties evaluated from thermotropic data of presently investigated newly
series-1 compared with series-A1 [41] and series-A2 [41] mention in Fig. 4. All three
series are similar with respect to presence of chalcone and allylidene amino linkage
group with varying alkyl side chain in left terminal end. The linearity and polarizability
of series-1 is higher as compare to other series-A1 and series-A2 due to the presence
one more phenyl ring joint through ester linkage group. Series-A1 and series-A2 shows
only nematic phase however present synthesized series display only SmC phase, this is
due to the presence of second ester (-COO-) linking group which more favors to smec-
tic phase as compare to nematic phase and also the effect of polarizability, polarity and

74
V. S. SHARMA ET AL.
Figure 5. Space filling diagram of structurally similar series.
Table 2: Average thermal stability in ꢀC.
Series
Series-1
Series-A1
Series-A2
SmC-I
SmC-N
Cr-N
Cr-SmC
N-I
150.0 (H4-H18
)
)
–
–
–
–
–
–
133.09 (C3-C18
)
)
138.5 (C4-C18
–
186.9 (C4-C18
)
)
129.3 (H4-H18
–
–
163.27 (C3-C18
(SmC-I ¼ smectic C to isotropic; SmC-N ¼ smectic C to nematic; Cr-N ¼ solid to nematic; Cr-SmC ¼ solid to smectic C;
N-I ¼ nematic to isotropic).
dipole moment of molecules. Thus, changing in liquid crystalline properties like thermal
stability and temperature range, commencement of mesophase will be influenced by the
magnitudes of changing structures of homologous series-1 as compare to series-A1 and
series-A2.
Figure 5 shows the space filling diagram of series-1, series-A1 and series-A2. It can be
seen that, the geometrical shape of all series are calamatic rod type. In series-A2 and
series-A3, molecules incorporated with four phenyl ring connected through three linking
unit while in series-1 one more phenyl rings and mesogenic unit is present. It is also
shown that present synthesised series-1 shows good thermal stability of mesophase as
compare to other two series-A1, -A2. Series-1 shows only smectic phase, this is due to
the formation of lamellar packing order in molecules to form smectic mesophase and
then passing through isotropic liquid without showing any nematic phase. However,
due to shorter molecular length of series-A1 and series-A2 as compare to series-1 to
exhibits no any lamellar packing arrangement of molecules and passing nematic phase
without showing smectogenic mesomorphism.
Thermal stability of present newly synthesised series-1, series-A1 and series-A2 are
listed in Table 2. From the Table 2, series-1 display only smectic mesophase with good
thermal stability while other two structurally similar series exhibited only nematic phase.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
75
Figure 6. Temperature range of phase transition in series-1, -A1, -A2.
Nematic thermal stability of series-A2 is higher as compare to series-A1 due to the pres-
ence of vinyl ester linking group which increase the molecular length as well as thermal
stability of mesophase. The temperature range of phase transition in present series-1
comparative with series-A1 and series-A2 is shown in Fig. 6. It can be seen that, total
temperature range of mesophase of series-A2 is higher as compare to series-A1 and ser-
ies-1.Temperature range of smectic to isotropic phase in comp.H4 and H5 is higher as
compare to higher member of compounds in series-1. Temperature range of series-A1 is
in between series-1 and series-A2 respectively. From, Fig. 6, it is also shown that the
commencement of mesophase in series-A1 is early (H3) as compare to series-1(H4) and
series-A2 (H4).These observations of series-1 are further established by using DSC ana-
lysis where phase transition associated with Cr-SmC, SmC-I phase transition.
3.1.4. Chemical reactivity
The nature of the electronic transition and frontier molecular orbital (FMO) distribu-
tions are investigated by using density functional theory (DFT) at the B3LYP/6-311 level
in Dichloromethane solution using the CPCM solvation model with default convergence
criteria. The calculated FMO distributions of comp.H1 and comp.H12 are presented in
Fig. 7 and Fig. 8. From Fig. 7, it is noted that the HOMO is localized on the phenyl-
allylidene amino unit while the LUMO is localized on chalconyl-phenyl unit. A close
examination of these orbitals reveals that the HOMO of comp.H1 from both series is
predominantly localized on the fourth phenyl unit with amino allylidene group while
the LUMO is mostly concentrated on chalconyl-phenyl group. Presence of allylidene
amino linking group shows significant influence on the HOMO orbitals however the
chalconyl group appearances impact on the LUMO orbitals. It can be noted that the
electronic properties of comp.H1, H12 (series-1) could have originated from the chal-
conyl and amino allylidene group inbuilt with phenyl ring. The HOMO-LUMO gap of
comp.H1 (series-1) is 2.294 eV which is higher as compare to comp.H12 (series-1). Thus,
the substitution of higher alkyl spacer chain in alkoxy group (-OR) may affect the
reactivity and stability of the compounds.

76
V. S. SHARMA ET AL.
Figure 7. The molecular orbitals and energies for the HOMO and LUMO of the comp.H1.
Figure 8. The molecular orbitals and energies for the HOMO and LUMO of the comp.H12.
3.2. DSC study
The thermal behaviour of mesogenic compounds was also investigated with DSC meas-
urements at heating and cooling scan rate of 10ꢀC min-1 under nitrogen atmosphere.
The phase transition temperatures obtained in DSC agree very well with POM observa-
tion. DSC thermographs of compounds H5, H6, H16, H18 are presented in Fig. 9.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
77
Figure 9. DSC thermograms of compound (a) H5; (b) H6; (c) H16; (d) H18 on heating.
All compounds are thermally stable as confirmed by the reproducibility of thermograms
on several heating and cooling cycles. In Fig. 9, compound H5 exhibits three endother-
mic peaks at 114.62ꢀC, 144.12 ꢀC and 178.61ꢀC in heating cycle, which correspondence
to the presence of crystal to crystal (Cr-Cr’), crystal to SmC (Cr’-SmC) and SmC-I
phase. That was further confirmed by POM analysis. While on cooling condition, again
these exothermic peaks were traced at 173.24 ꢀC, 143.68ꢀC and 115.61ꢀC. Compound
H6 exhibits three endothermic peaks at 103.91 ꢀC, 142.52ꢀC and 163.64ꢀC on heating
cycle correspondence to crystal to crystal, crystal to SmC and SmC to isotropic phase
while on cooling cycle; it appears at 161.58 ꢀC, 138.32ꢀC and 106.78ꢀC. Compound H16
shows three endothermic peaks at 88.67 ꢀC, 111.24ꢀC and 132.12ꢀC on heating cycle
which reveals with POM results. On cooling cycle, again this exothermic peak exhibits
at 134.68 ꢀC, 112.94ꢀC and 82.34ꢀC. Compound H18 shows three endothermic peaks at
79.92 ꢀC, 105.74ꢀC and 124.72ꢀC in heating condition while on cooling condition it
appears at 125.01ꢀC, 101.69ꢀC and 80.64ꢀC. The phase transition temperatures, enthalpy
and entropy values for the present synthesized series are summarized in Table 3.
3.3. XRD study
The mesophase structures of novel chalconyl amino allylidene ester LCs were further
confirmed by X-ray diffraction (XRD) studies of comp.H5 and H8 filled in Lindemann
capillaries. The XRD pattern obtained for comp.H5 and H8 at 146.0ꢀC and 139.0ꢀC for

78
V. S. SHARMA ET AL.
Table 3: Transition temperature (ꢀC) and enthalpy (kJ/mol) and entropy change (J molꢁ1kꢁ1) by DSC measurement.
Comp.
Transition
Heating scan(ꢀC)
Cooling scan(ꢀC)
DH
DH
DS
DS
H5
Cr-Cr’
Cr’-SmC
SmC-I
Cr-Cr’
Cr’-SmC
SmC-I
Cr-Cr’
Cr’-SmC
SmC-I
Cr-Cr’
Cr’-SmC
SmC-I
114.62
144.12
178.61
103.61
142.52
163.64
88.67
111.24
132.12
79.92
115.61
143.68
173.24
106.78
138.32
161.58
82.34
112.94
134.68
80.64
4.82
12.92
7.21
5.32
21.24
7.32
3.16
19.65
7.87
8.56
3.42
11.34
3.82
9.56
7.43
8.82
7.23
10.42
9.02
6.45
12.43
5.32
0.0124
0.0309
0.0159
0.0141
0.0511
0.0167
0.0087
0.0511
0.0194
0.0242
0.0387
0.0186
0.0088
0.0272
0.0085
0.0251
0.0180
0.0194
0.0088
0.0269
0.0221
0.0182
0.0331
0.0133
H6
H16
H18
105.74
124.72
101.69
125.01
14.67
7.41
(Cr-Cr’ ¼ solid to solid crystal; Cr-SmC ¼ solid to SmC; Cr-N ¼ solid to nematic; N-I ¼ nematic to isotropic).
Figure 10. XRD patterns of compound H5 at 146ꢀC.
the smectic C phase are shown in Fig. 10 and Fig. 11. The sharp reflection in the small
angle region with d-spacing 34.21 Å of comp.H8 and 33.04 Å of comp.H5. No any dif-
fuse peak at wide angle region in both compound. In comp.H8, the layer spacing of
34.21Å in the smectic C phase is slightly smaller than the molecular length of 37.05 Å
while in comp.H5; the layer spacing of 33.04 Å in the smectic phase is smaller than its
molecular length 35.31Å, indicating the tilted organization of the molecules in the
layers. Figure 12 represents the proposed mechanism to indicate the arrangement of
lamellar packing in molecules to exhibit SmC phase in present series-1. Higher member
compounds display smectic C property at lower temperature as compare to lower mem-
ber of present series because of the long aliphatic methylene group increasing the flexi-
bility, polarity, polarizability of molecules to induce mesophase at lower transition
temperature.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
79
Figure 11. XRD patterns of compound H8 at 139ꢀC.
Figure 12. Propose mechanism of present series-1.
4. Conclusion
In summary, we have reported the synthesis and phase behaviour of presently new
homologous series containing five aromatic rings connected to four mesogenic unit as
central part. A new calamatic rod type homologous series of chalcone derived LCs com-
pounds possessing allylidene amino and ester linking unit at central part and other end

80
V. S. SHARMA ET AL.
with variable chain lengths. The nature of the mesophases has been established by using
POM, DSC and XRD studies. The lower member H1 to H3 shows non mesogenic
behaviour due to presence of short alkyl spacer in n-alkyl chain. Comp.H4 to H18 shows
enantiotropic smectic C phase with good temperature range.
Acknowledgment
VS acknowledge thanks to Department of Chemistry, Faculty of Basic and Applied Science,
Madhav University for providing lab facility. Authors are also thankful to NFDD Centre for pro-
viding analytical and spectral services. Authors thanks to Miss Akshara Shah (Department of
Chemistry, Mumbai University) for helping fruitful discussion in high temperature XRD analysis.
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