New hockey stick shaped amino allylidene (?N?CH?CH?CH) based compounds: Effect of linkage group on mesomorphic properties

Article abstract of DOI:10.1080/15421406.2017.1357430

Two nonlinear hockey stick shaped homologous series based on three linking groups have been synthesized and characterized by elemental analyses and spectroscopic techniques. The mesomorphic properties of these compounds were observed by polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). In this present investigation, we have synthesized two homologous series viz. 2-((3-phenyl allylidene) amino) phenyl 4-((4-n-alkoxy benzylidene) amino) benzoate (series-1) and 4-((2-((3-phenyl allylidene) amino) phenoxy) carbonyl) phenyl-4-n-alkoxy benzoate (series-2). Both the series are differing with respect to first linking group. In series-1, comp.C₄-C₁₈ shows nematic as well as smectic phase while in series-2, comp.C₁₀-C₁₆ shows smectic and nematic phase while comp.C₄-C₁₈ shows only nematic phase.

Full text of DOI:10.1080/15421406.2017.1357430

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
New hockey stick shaped amino allylidene
(‒N˭CH‒CH˭CH) based compounds: Effect of
linkage group on mesomorphic properties
Vinay. S. Sharma, Rajesh. H. Vekariya, Anuj. S. Sharma & R. B. Patel
To cite this article: Vinay. S. Sharma, Rajesh. H. Vekariya, Anuj. S. Sharma & R. B. Patel
(
2017): New hockey stick shaped amino allylidene (‒N˭CH‒CH˭CH) based compounds: Effect
of linkage group on mesomorphic properties, Molecular Crystals and Liquid Crystals, DOI:
0.1080/15421406.2017.1357430
1
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Published online: 12 Sep 2017.
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Date: 14 September 2017, At: 03:44

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
https://doi.org/./..
New hockey stick shaped amino allylidene (–N=CH–CH=CH)
based compounds: Effect of linkage group on mesomorphic
properties
a
b
b
a
Vinay. S. Sharma , Rajesh. H. Vekariya , Anuj. S. Sharma , and R. B. Patel
a
Chemistry Department, K. K. Shah Jarodwala Maninagar Science College, Gujarat University, Ahmedabad,
b
Gujarat, India; Department of Chemistry, School of Science, Gujarat University, Ahmedabad, Gujarat, India
ABSTRACT
KEYWORDS
Two nonlinear hockey stick shaped homologous series based on three
linking groups have been synthesized and characterized by elemental
analyses and spectroscopic techniques. The mesomorphic properties
of these compounds were observed by polarizing optical microscopy
Hockey-stick; liquid crystals;
nematic; smectic
(POM) and differential scanning calorimetry (DSC). In this present inves-
tigation, we have synthesized two homologous series viz. 2-((3-phenyl
allylidene) amino) phenyl 4-((4-n-alkoxy benzylidene) amino) benzoate
(
series-1) and 4-((2-((3-phenyl allylidene) amino) phenoxy) carbonyl)
phenyl-4-n-alkoxy benzoate (series-2). Both the series are differing with
respect to first linking group. In series-1, comp.C –C shows nematic
4
18
as well as smectic phase while in series-2, comp.C –C shows smectic
and nematic phase while comp.C –C shows only nematic phase.
1
0
16
4
18
GRAPHICAL ABSTRACT
1
. Introduction
The design of novel thermotropic liquid crystals as advanced functional materials involves
suitable selection of a core fragment, linking group, and terminal functionality. However,
anisometric rodlike or disk-like shaped molecules used to be a fundamental prerequisite for
conventional thermotropic liquid crystal formation, because steric packing considerations
play an important role in this interesting state of soft matter [1–2].
CONTACT Vinay. S. Sharma
Science College, Gujarat University, Ahmedabad , Gujarat, India.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gmcl.
 Taylor & Francis Group, LLC
vinaysharma@gmail.com
Chemistry Department, K. K. Shah Jarodwala Maninagar
©

2
V. S. SHARMA ET AL.
A large number of bent-core or banana-shaped mesogens have been synthesized to exam-
ine their mesophase structures [3–4]. Afterwards, several groups reported the synthesis of
new liquid crystal compounds with various molecular shapes like T, H, and W [5–6]. In
the last period, a special kind of nonsymmetrical bent-shaped liquid crystal of hockey stick
form was developed and these compounds are considered at the borderline between bent-
core and rodlike mesogens [7]. A helical chiral smectic A phase undergoing a first order
transition to a ferroelectric smectic C phase was observed for a hockey stick molecule of a
four phenyl ring system having an ester of chiral 2-octanol pointing to the lateral side group
direction [8].
Samulski et al. studied the structural variations on a series of all aromatic liquid crystals
derived from p-quinquephenyl, including hockey stick and boomerang shaped liquid crystals
[
9]. Choi and his groups reported asymmetric bent-core liquid crystals with 1,6-napthalene
central unit to form B mesophase [10]. Sedative’s group reported that asymmetric banana-
2
shaped molecules with a strongly polar terminal cyano/nitro group showed a polar biaxial
smectic A phase [11]. Gallardo et al. reported unsymmetrical luminescent hockey stick shaped
compounds and studied their LCs properties [12]. Subsequently, Dhara and his coworkers
studied the measurement of birefringence, dielectric constant, splay, bend elastic constant,
and rotational viscosity in the nematic phase (N) of a hockey stick shaped compound exhibit-
ing smectic A and anticlinic smectic C phase [13]. Scutaru reported the hockey stick shaped
liquid crystals based on a 2,5-asymmetric disubstituted [1,3,4] oxadiazole core [14]. Seltmann
et al. reported low temperature enantiotropic nematic phase from V-shaped molecules [15].
Afterward, Yoshizawa reported synthesis and physical properties of T-shaped chiral liquid
crystal oligomers having terminal cyano (–CN) groups [16]. Stannarius and other groups
studied the several unusual behaviors in the LC phase formed by hockey stick molecules.
An anticlinic structure is confirmed for a lower temperature smectic C phase on free standing
films of hockey stick molecules consisting of schiff base and cinnamate or benzoate linkage
groups [17]. Yu et al. reported enantiotropic anticlinic smectic C (SmCa), smectic C (SmC),
smectic A (SmA), and nematic (N) phases of hockey stick shaped molecules [18]. Sadashiva
and his groups synthesized a series of five ring compounds composed of hockey stick shaped
molecules and studied their mesomorphic properties. They have reported all the synthesized
compounds display anticlinic smectic C phase [19]. Furthermore, Svoboda et al. reported
hockey stick mesogens and identified nematic, synclinic, and anticlinic smectic C phase [20].
Prasad et al. reported azo based hockey stick shaped compounds and studied the effect of dif-
ferent types of linkages and their direction of linking on the mesomorphic properties [21].
Consequently, Das et al. reported hockey stick shaped compounds with lateral methyl group
showing nematic, synclinic, and anticlinic smectic C phases [22]. Clark et al. reported chiral
random grain boundary phase of achiral hockey stick liquid crystals [23]. Recently, Jasinski
et al. reported a series of hockey stick shaped 6-oxoverdazyl radicals containing –CF and
3
–
CN group to exhibited nematic phase [24].
In this work, we present the synthesis of unsymmetrical hockey stick shape type two
homologous series-1 and series-2 along with their mesomorphic properties. The structure
of final target compounds of series-1 and series-2 is shown in below Fig. 1.
2
. Experimental
2.1. General
For the synthesis of target compounds in homologous series-1 and series-2, the following
materials were used: 4-hydroxy benzoic acid, 4-hydroxy benzaldehyde were purchased from

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
3
Figure . Chemical structure of final synthesized series- and series-.
SRL (Mumbai), alkyl halides were purchased from Lancaster (England), 4-amino benzoic
acid was purchased from Sigma Aldrich, anhydrous K CO , KOH, 4-amino phenol, cin-
2
3
namaldehyde were 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
were dried and distilled prior to use. The molecular structures of the target products and the
intermediates were confirmed by spectroscopic analysis and elemental analysis. Representa-
1
tive homologous series were characterized by elemental analysis, infrared spectroscopy, H
1
NMR spectra. IR spectra were recorded by Perkin–Elmer spectrum GX, H NMR spectra
were recorded on Bruker (400 MHz) using CDCl as solvent. Microanalysis was performed
3
on Perkin–Elmer PE 2400 CHN analyzer. Texture image of nematic phase was determined by
using miscibility method. Transition temperature and LC properties (textures) were deter-
mined using an polarizing optical microscopy (POM) equipped with heating stage attached
with camera. Decomposition temperatures were determined using Shimadzu differential
−1
Scanning Calorimeter (DSC) with a heating rate of 5 °C–10.0 °C min .
2
.2. Synthesis of series-1 and series-2 compounds
... Synthesis of -((-phenyl allylidene amino) phenol (a)
2
-((3-phenyl allylidene amino) phenol was prepared by reported method [25]. (Brownish yel-
−1
low color, Yield: 78%), IR (KBr): vmax cm 3030 (C–H str.), 1590 (CH=N), 961 (–CH=CH–),
3
280 (–OH str.). Elemental analysis: calculated for C H ON: C, 80.71; H, 5.82; N, 6.27%;
15 13
found: C, 80.62; H, 5.73; N, 6.23%.
... Synthesis of -n-alkoxy benzoic acid (a)
4
-n-alkoxy derivatives of benzoic acid were prepared by reported method [26].

4
V. S. SHARMA ET AL.
... 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 H SO and reaction mixture was refluxed for 2–3 hr. Then
2
4
reaction mixture was dumped into ice, and allowed it to settle down. Solid white precipitate
of methyl-4-hydroxy benzoate was obtained. Product was filtered, washed, dried, and then
purified by alcohol. Fine crystals were obtained (M.P.126 °C, yield 72%) [27].
ꢀ

4
... Synthesis of -(methoxy carbonyl) phenyl  -n-alkoxy benzoate (b)
ꢀ
-(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)
0.246 g, 2.02 mmol); dicyclohexyl carbodiimide (DCC) (0.457 g, 2.22 mmol) and dimethy-
laminopyridine (DMAP) in catalytic amount (0.002 g, 0.2 mmol) in dry CH Cl (DCM)
(
2
2
(
60 ml) was stirred at room temperature for 48 hr. The white precipitate of DCU was obtained
which was isolated by filtration and removed, 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) [28].
−1
Comp. 3b IR (KBr): v
cm 3033 (C–H str.), 679 polymethylene group of –OC H
4
:
max
4
9
1
chain group, 1740 (–COO– group), 1240 (C–O str.). H NMR: 0.88 (t, 3 H, –OC H ), 4.06
4
9
(
t, 2 H, –OC H ), 3.82 (s, 3 H, –OCH ), 1.43–1.72 (p, 4 H, –OC H ), 7.12 & 8.01 (d, 4 H,
4 9 3 4 9
first phenyl ring), 7.38 & 8.11 (d, 4 H, second phenyl ring). Elemental analysis: calculated for
C H O : C, 69.51; H, 6.09; found: C, 69.41; H, 5.91; O, 5.89%.
19
20
5
ꢀ

4
... Synthesis of -(( -n-alkoxy benzoyl) oxy) benzoic acid (c)
ꢀ
-((4 -n-alkoxy benzoyl) oxy) benzoic acid were prepared by dissolving compound 3b in
ethanol (40 ml) and 10% aq. NaOH (2 ml) was added. The resultant mixture was heated at
reflux for 6–7 hr, 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 [29].
−1
Comp. 3c IR (KBr): v cm , 3071 (C–H str.), 3301 (–OH of carboxylic group), 1680
4
:
max
(
C=O str. of carboxylic group), 1750 (–COO– group), 648 polymethylene group of –OC H
4
9
1
group. H NMR: 0.88 (t, 3 H, –OC H ), 4.06 (t, 2 H, –OC H ), 10.8 (s, 1 H, –COOH group),
4
9
4
9
1
.43–1.72 (p, 4 H, –OC H ), 7.11 & 8.01 (d, 4 H, first phenyl ring), 7.58 & 8.23 (d, 4 H, second
4 9
phenyl ring). Elemental analysis: calculated for C H O : C, 68.78; H, 5.73%; found: C, 68.69;
18
18
5
H, 5.68%.

4
... Synthesis of -n-alkoxy benzaldehyde (a)
-n-alkoxy benzaldehyde (4a) were synthesized by refluxing the mixture of 4-hydroxy ben-
zaldehyde (1 equiv.) with corresponding n-alkyl bromide (R-Br) (1 equiv.) in presence of
anhydrous K CO (1.2 equiv.) in dry acetone as a solvent [30]
2
3
ꢀ

... Synthesis of -(( -n-alkoxy benzylidene) amino) benzoic acid (b)
4
-((4-alkoxy benzylidene) amino) benzoic acid were prepared by refluxing the mixture of 4a
and 4-amino benzoic acid at 3–4 hr in presence of ethanol and few drops of glacial acetic acid.
The resultant mixture was filtered, dried, and recrystallized from ethanol [25].
−1
Comp.4b : FT-IR (KBr) in cm : 3032 (–C–H– str in aromatic), 2825(C–H str. –OCH ),
1
3
1
365 and 1236 (–C–O Str), 806 (disubstituted aromatic ring -para), 1630 (–CH=N, str.
1
azomethine group), 1667 (–C=O Str.), 2550 (–OH of –COOH group). H NMR: δH (CDCl ,
3
4
00 MHz): 3.80 (s, 3 H, –CH of –OCH group), 10.32 (s, 1 H, –OH group of –COOH), 8.23
3 3

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
5
(
s, 1 H, –CH=N– group), 7.01–7.82 (4 H, first phenyl ring), 7.42–8.14 (4 H, second phenyl
ring); Elemental analysis of C H NO : Calculate: C, 70.58%; H, 5.09%; O, 18.82%; N, 5.49%;
15
13
3
found: C, 69.62%; H, 4.96%; O, 18.74%; N, 5.42%.
−
1
Comp.4b : FT-IR (KBr) in cm : 3031 (–C–H– str in aromatic), 681 (Polymethylene
1
0
(
1
–CH -)n of –OC H ), 1355 and 1230 (–C–O str), 821 (disubstituted aromatic ring -para),
2 10 21
1
630 (–CH=N, Str. azomethine group), 1661 (–C=O Str.), 2556 (–OH of –COOH group). H
NMR: δH (CDCl , 400 MHz): 0.88 (t, 2 H, –OC H group), 1.31 (q, 3 H, –OC H group),
3
10 21
10 21
1
.26–1.29 (m, 12 H, –OC H group), 1.71 (P, 2 H, –OC H group), 4.06 (t, 2 H, –OC H
10 21 10 21 10 21
group), 10.48 (s, 1 H, –OH group of –COOH), 8.23 (s, 1 H, –CH=N– group), 7.06–7.82 (4 H,
first phenyl ring), 7.43–8.14 (4 H, second phenyl ring); Elemental analysis of C H NO : Cal-
24
31
3
culate: C, 75.59%; H, 8.13%; O, 12.59%; N, 3.67%; found: C, 75.32%; H, 8.02%; O, 12.52%; N,
.62%.
Comp.4b : FT-IR (KBr) in cm : 3032 (–C–H– str in aromatic), 1365 and 1236 (–C–O
3
−1
1
2
str), 644 Polymethylene (–CH -)n of –OC H , 808 (disubstituted aromatic ring -para), 1631
2
12 25
1
(
–CH=N, str. azomethine group), 1672 (–C=O Str.), 2558 (–OH of –COOH group); H
NMR: 0.88 (t, 2 H, –OC H group), 1.31 (q, 3 H, –OC H group), 1.26–1.29 (m, 14 H,
12
25
12 25
–
OC H group), 1.71 (P, 2 H, –OC H group), 4.06 (t, 2 H, –OC H group), 10.68 (s,
12 25 12 25 12 25
1
H, –OH group of –COOH), 8.21 (s, 1 H, –CH=N– group), 7.04–7.81 (4 H, first phenyl
ring), 7.43–8.14 (4 H, second phenyl ring); Elemental analysis of C H NO : Calculate: C,
26
35
3
7
6.28%; H, 8.55%; O, 11.73%; N, 3.42%; found: C, 76.23%; H, 8.48%; O, 11.68%; N, 3.37%.
... General procedure for the synthesis of (series-)
The compound has been prepared by esterification of the appropriate compound 4b
(
(
2.02 mmol) and compound 1a (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 CH Cl (DCM) (40 ml) was stirred at room temperature for 48 hr. The
2 2
slightly yellowish white precipitate of DCU was obtained which was isolated by filtration and
removed, while the filtrate was evaporated to dryness. The resultant crude residue was puri-
fied by column chromatography on silica gel eluting with methanol:chloroform as eluent (1:4)
[
31]. The synthesis route of derivatives for series-1 and series-2 were mentioned in Schemes 1
and 2.
C (series-1): IR (KBr): v
cm 1 3066 (C–H str. of alkane), 1601 (C=C str. of alkene
−
4
max
in amino allylidene), 1630 (–CH=N-), 1740 (–COO– group), 992 (C–H bending of alkene),
1
170 (C–O str. of ether linkage of butoxy group), 791 (polymethylene group of –OC H ).
4 9
1
H NMR: 0.90 (t, 3 H, –CH of polymethylene –OC H ), 1.45 (p, 2 H, –OC H ), 1.76(p,
3
4
9
4
9
2
6
(
H, –OC H ), 4.06 (t, 2H, –OC H ), 8.02 (s, 1H, –CH=N-), 7.48 (s, 1H, –N=CH–CH=C–),
4
9
4
9
.84 & 7.21 (d, 2H, –N=CH–CH=CH–), 7.07 & 7.82 (d, 4H, first phenyl ring), 7.34 & 8.21
d, 4H, second phenyl rin), 7.37, 7.40 & 7.51 (d, 4H, third phenyl ring), 7.60, 7.33, 7.40 (d,
5
5
H, fourth phenyl ring). Elemental analysis: calculated for C H N O : C, 78.88; H, 5.97; N,
33 30 2 3
.57%; found: C, 78.81; H, 5.91; N, 5.51%.
cm 1 3063 (C–H str. of alkane), 1601 (C=C str.
−
C (series-1): IR (KBr):: IR (KBr): v
5
max
of alkene in amino allylidene), 1630 (–CH=N-), 1740 (–COO– group), 991 (C–H bending
of alkene), 1170 (C–O str. of ether linkage of pentoxy group), 761 (polymethylene group
1
of –OC H ). H NMR: 0.90 (t, 3H, –CH of polymethylene –OC H ), 1,29–1.45 (m, 4H,
5
11
3
5
11
–
–
OC H ), 1.76(p, 2H, –OC H ), 4.06 (t, 2H, –OC H ), 8.01 (s, 1H, –CH=N-), 7.47 (s, 1H,
5
11
5
11
5
11
N=CH–CH=C–), 6.84 & 7.20 (d, 2H, –N=CH–CH=CH–), 7.07 & 7.81 (d, 4H, first phenyl
ring), 7.34 & 8.21 (d, 4H, second phenyl ring), 7.37, 7.40 & 7.52 (d, 4H, third phenyl ring),

6
V. S. SHARMA ET AL.
7
7
.60, 7.33, 7.40 (d, 5H, fourth phenyl ring). Elemental analysis: calculated for C H N O : C,
9.06; H, 6.20; N, 5.42%; found: C, 78.98; H, 6.14; N, 5.39%.
33
27
2
3
... General procedure for the synthesis of (series-)
The compound has been prepared by esterification of the appropriate compound 3c
(
(
2.02 mmol) and compound 1a (0.246g, 2.02 mmol); dicyclohexylcarbodiimide (DCC)
0.457 g, 2.22 mmol) and dimethylaminopyridine (DMAP) in catalytic amount (0.002 g,
0
.2 mmol) in dry CH Cl (DCM) (40 mL) was stirred at room temperature for 48 hr. The
2 2
slightly off white precipitate of DCU was obtained which was isolated by filtration and dis-
carded, while the filtrate was evaporated to dryness. The resultant crude residue was purified
by column chromatography on silica gel eluting methanol:chloroform (1:4) [31].
−1
C (series-2): IR (KBr): IR (KBr): v
6
cm 3040 (C–H str. of alkane), 1604 (C=C str.
max
of alkene in amino allylidene), 1640 (–C=O str.), 1730 (–COO– group), 991 (C–H bend-
ing of alkene), 1130 (C–O str. of ether linkage of hexyloxy group), 663 (polymethylene
1
group of –OC H ). H NMR: 0.88–0.90 (t, 3H, –CH of polymethylene –OC H ), 1.29–
6
13
3
6
13
1
7
.43 (m, 6H, –OC H ), 1.76 (p, 2H, –OC H ), 4.06 (t, 2H, –OCH –CH - of –OC H ),
6 13 6 13 2 2 6 13
.48 (s, 1H, –N=CH–CH=C–), 6.83 & 7.21 (d, 2H, –N=CH–CH=CH–), 7.12 & 8.12 (d, 4H,
first phenyl ring), 7.52 & 8.27 (d, 4H, second phenyl ring), 7.31, 7.40 & 7.52 (d, 4H, third
phenyl ring), 7.33, 7.40, 7.58 (d, 5H, fourth phenyl ring). Elemental analysis: calculated for
C H NO : C, 76.78; H, 6.03; N, 2.55%; found: C, 76.71; H, 5.97; N, 2.48%.
3
5
33
5
−1
C (series-2): IR (KBr): IR (KBr): v
cm 3040 (C–H str. of alkane), 1610 (C=C str.
8
max
of alkene in amino allylidene), 1640 (–C=O str.), 1750 (–COO– group), 991 (C–H bending
of alkene), 1130 (C–O str. of ether linkage of octyloxy group), 781 (polymethylene group
1
of –OC H ). H NMR: 0.88–0.90 (t, 3H, –CH of polymethylene –OC H ), 1.26–1.43 (m,
8
17
3
8
17
1
0H, –OC H ), 1.76 (p, 2H, –OC H ), 4.06 (t, 2H, –OCH –CH - of –OC H ), 7.49 (s, 1H,
–
8 17 8 17 2 2 8 17
N=CH–CH=C–), 6.84 & 7.21 (d, 2H, –N=CH–CH=CH–), 7.12 & 8.10 (d, 4H, first phenyl
ring), 7.52 & 8.27 (d, 4H, second phenyl ring), 7.31, 7.40 & 7.52 (d, 4H, third phenyl ring),
7
7
.33, 7.40, 7.58 (d, 5H, fourth phenyl ring). Elemental analysis: calculated for C H NO : C,
37 37 5
7.21; H, 6.43; N, 2.43%; found: C, 77.19; H, 6.41; N, 2.39%.
−1
C10 (series-2): IR (KBr): vmax cm 3030 (C–H str. of alkane), 1604 (C=C str. of alkene
in amino allylidene), 1630 (–C=O str.), 1750 (–COO– group), 991 (C–H bending of
alkene), 1140 (C–O str. of ether linkage of decyloxy group), 804 (polymethylene group of –
1
OC H ). H NMR: 0.88–0.90 (t, 3H, –CH of polymethylene –OC H ), 1.26–1.43 (m, 14H,
10
21
3
10 21
–
–
OC H ), 1.76 (p, 2H, –OC H ), 4.06 (t, 2H, –OCH –CH - of –OC H ), 7.50 (s, 1H,
10 21 10 21 2 2 10 21
N=CH–CH=C–), 6.85 & 7.21 (d, 2H, –N=CH–CH=CH–), 7.12 & 8.10 (d, 4H, first phenyl
ring), 7.51 & 8.27 (d, 4H, second phenyl ring), 7.31, 7.40 & 7.52 (d, 4H, third phenyl ring),
7
7
.33, 7.40, 7.58 (d, 5H, fourth phenyl ring). Elemental analysis: calculated for C H NO : C,
7.61; H, 6.79; N, 2.52%; found: C, 77.56; H, 6.73; N, 2.48%.
39 41 5
2
.3. Reaction scheme
3
. Result and discussion
In the present study, we have synthesized thirteen compounds for each two series, 2-((3-
ꢀ
phenyl allylidene) amino) phenyl 4-((4 -n-alkoxy benzylidene) amino) benzoate (series-1)
ꢀ
and 4-((2-((3-phenyl allylidene) amino) phenoxy) carbonyl) phenyl 4 -n-alkoxy benzoate
(series-2) were synthesized and their mesomorphic properties were studied by using DSC
and POM.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
7
Scheme . Synthetic route of some derivatives of series- and series-.
3.1. POM investigation
We have studied comprehensively the effect of linking group as well as alkyl aliphatic chain
length to form mesogens having hockey stick type shape. It has been proven that altering the
length of alkyl chain effects the LC property. Here, in present, we have synthesized and studied
the effect of linking group as well as the effect of varying aliphatic side alkyl chain length from
small spacer (–OCH ) to higher spacer (–OC H ) in presence of four benzene ring con-
3
18 37
nect by three linking groups. We have synthesized thirteen homologous compounds (C –C ,
1
8
C , C , C , C ) in both homologous series-1 and series-2. All the synthesized compounds,
12
14
16
18
except for three derivatives (C –C ) exhibit LC phases in both series. However, the type of
1
3
the mesophases depends on the number of carbon atoms in the aliphatic spacer and terminal
alkyl chain. Nematic mesophase commences from C homologue in both synthesized series.
4
Smectic mesophase commences early in series-1 as compared to series-2. The transition tem-
perature of series-1 and series-2 are listed below in Tables 1 and 2.
Compounds C –C in both series do not show in LC property. This is due to the presence
1
3
of short alkyl spacer or tail group in left side chain which causes more crystallinity tendency
and directly passes isotropic without displaying LC phase. The nonmesomorphicity of com-
pound is mainly attributed to the low magnitudes of intermolecular dispersion forces and

8
V. S. SHARMA ET AL.
Scheme . Synthetic route of series- and series-.
Table . Transition Temperature in °C by POM (series-).
Transition temperatures in C
Nematic
Sr.no
R = n-alkyl group
Cr
Smectic
Isotropic
.

C
C
C
C
C
C
C
C
C
C
C
C
C
·
·
·
·
·
·
·
·
·
·
·
·
·
—
—
—
—
—
—
—
—
—
·
·
·
·
·
·
·
·
·
·
·
·
·






.
.
.
.
.
.
.
.
.
.
.
.
—
·
—
—
·
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
·
·
·
·
·
·


·
·
·
·








·
·
·
·
.
.
·
·
·
·

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
9
Table . Transition Temperature in °C by POM (series-).
Transition temperatures in C
Sr.no
R = n-alkyl group
Cr
Smectic
Nematic
Isotropic

C
C
C
C
C
C
C
C
C
C
C
C
C
·
·
·
·
·
·
·
·
·
·
·
·
·
—
—
—
—
—
—
—
—
.
.
.
.
—
—
—
—
—
—
—
—
—
·
—
—
—
—
—
.
.
.
.
.
.
.
.
.
.
.
.
.
·
·
·
·
·
·
·
·
·
·
·
·
·












—
·
.
.
.
.
.
.
.
.
.
.
·
·
·
·
·



·
·
·
·
·
·

·
·
low magnitudes of dipole-dipole interactions leading to its high crystallizing tendency which
origins abrupt breaking of crystal lattices due to unsuitable and unfavorable magnitudes of
anisotropic forces of intermolecular attractions. Thus, irregular breaking of crystal lattices
suddenly takes place at relatively higher temperature. As a result, crystalline solid state directly
passes into isotropic state without displaying LC phase. The phase diagram of both the series
are listed in Figs. 2 and 3.
A phase diagram (Fig. 2) of new series-1 consisted of Cr-N/I, Sm-N, and N-I transition
curves showing phase behaviors of series. The Cr-N/I transition curve starts decreasing from
first C homologue to C homologue, increasing at C homologue, and again decreasing upto
1
6
7
last C18 homologue. Odd-even effect is present between C to C homologue in series-1,
6
7
respectively. Sm-N transition curve show increasing tendency at C and C homologue with
5
7
overall downward tendency. N-I transition curve shows decreasing tendency from C1 to C6
homologue and then increases at C homologue and then continue to decreases upto last C
7
18
homologue. It is interesting to note that the altering of alkyl chain length on alkoxy side group
(
–OR) effects the mesomorphic properties of synthesized compounds.
Figure . Phase diagram of series-.

1
0
V. S. SHARMA ET AL.
Figure . Phase diagram of series-.
The phase diagram of series-2 is mentioned in below Fig. 3. Cr-M/I and N-I transition
curves show decreasing tendency from lower member (C ) to higher member (C ) com-
1
18
pounds except C homologue in series-2. Odd-even effect is observed in Cr-M/I and N-I
7
transition curve at C –C homologue. Sm-N transition curve starts from C homologue and
6
7
10
shows decreasing tendency upto last C16 homologue. The exhibition of nematic mesophase
in C –C (series-1, series-2) is attributed to the appropriate magnitudes of end to end
4
18
intermolecular anisotropic forces of attractions and closeness as a significance of favorable
molecular rigidity, linearity due to the presence of linking group, and flexibility caused by
the presence of left side chain generate permanent dipole-moment across the long molecular
axis, suitable magnitudes of dispersion forces and dipole-dipole interactions, molecular
polarizability, and polarity which facilitate the molecules under microscopic study to float on
the surface with statically parallel orientational order within certain range of temperature as
nematic phase [32].
3
.2. Nematic mesophase study by miscibility method
The nematic mesophase in comp. C –C were also confirmed by using miscibility method
4
18
which was listed in Table 3. Comp.C10 shows threaded type nematic phase whereas in
comp.C , rod type textural image was seen. Comp. C homologue shows rod type textu-
12
14
ral pattern of nematic phase. Comp.C –C shows threaded type textural pattern of nematic
16
18
mesophase.
Table . Texture of Nematic Phase of C , C , C and C by miscibility method.

 ,

Sr. No.
Homologue
Texture (Series-)
Texture (Series-)

C
C
C
C
Threaded
Threaded
Schlieren
Schlieren
Threaded
Threaded
Threaded
Rodlike




MOLECULAR CRYSTALS AND LIQUID CRYSTALS
11
Figure . Photomicrograph of optical texture of (a) C10 at . °C (series-); (b) C16 at . °C (series-); (c)
C14 at . °C (series-); (d) C6 at . °C (series-).
3
.3. 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 Figs. 4 and 5, a schlieren type nematic tex-
ture pattern of compound C (series-1) is seen at 131.0 °C. Compound C show schlieren
10
16
type texture image of nematic pattern at 107.0 °C on heating condition. Compound C6
series-1) shows textural pattern of smectic A phase at 102.0 °C on heating condition. Com-
pound C (series-1) shows feather like textural pattern of smectic A phase at 91.0 °C on cool-
(
14
ing condition. Compound C (series-2) shows broken focal type textural pattern of smectic
10
Figure . Photomicrograph of optical texture of (a) C10 at . °C (series-); (b) C14 at . °C (series-).

1
2
V. S. SHARMA ET AL.
Figure . Space filling diagram of structurally similar analogous series.
A phase at 116.0 °C on heating condition, while compound C shows typical textural pattern
14
of smectic C phase at 108.0 °C on heating condition. The focal conic texture pattern appears
broken in the SmC mesophase because of the disruption of the lamellar packing due to the
tilt of the molecules [33].
3
.4. Comparative study
Here, we have compared the geometry and molecular shape with respect to linking and ter-
minal groups of presently synthesized series-1 with series-2. The structure of both the series
is mentioned in above Fig. 1. The hockey stick shaped homologous series-1 and series-2 are
identical with respect to four phenyl rings and three linkage groups that connect one part
of a core to another part. But they differ with respect to each other at first linkage group
between first and second phenyl ring. In series-1, schiff base (–CH=N-) linkage group is
present while in series-2, ester (–COO–) group is present. The geometrical shape of series-2
is more steady as compared to series-1 because of the presence of ester (–COO–) unit which
confers a stepped structure and maintain the linearity of molecule and due to its high polarity
mesophase observed at higher temperature as compared to series-1. There is conjugation in
imine (–CH=N-) linkage group which extended over the longer molecule and enhance the
polarizability anisotropy of molecule. Thus, variations in mesomorphic (LC) properties are
ascribed to the magnitudes of differing features like (shapes and left terminal tail groups) in
both series from lower chain containing homologue to higher chain containing homologue.
The space-filling diagram indicate the energy minimize in series-1 and series-2 as shown
in Fig. 6. The geometrical shapes of both series are nonlinear. Presence of allylidene amino
unit (-N=CH–CH=CH–) and second ester (–COO–) part unit is common in both series.
Therefore, it proves that, the changing in first linking unit ester (–COO–, series-1) by schiff
base (–CH=N–, series-2) as a result variation is arrised in LC properties. The ester (–COO–)
linkage group is a polar group that can aid lamellar packing and create smectic phase in both
series [34].

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
13
Table . Relative thermal stability in °C.
Series
Series-
Series-
Sm-N
N-I
.
.
. °C
C–C
C –C
. °C
C–C
C–C
Commencement of nematic phase
Commencement of smectic phase
Total temperature range of mesophase


.–. C C
.–. C C


 
3
.5. Thermal stability and temperature range of mesophase
Table 4 represents some thermometric data of series-1 and series-2 in comparative manner.
Thermal stability of nematic mesophase of series-1 is lower as compared to series-2. Thermal
stability of smectic phase of series-1 is greater as compared to series-2. Temperature range of
mesophase is in increasing order of lower to higher homologue in series-1 and series-2. The
early or late commencement of mesophase depends upon the extent of molecular noncopla-
narity caused by the presence of linkage group and their magnitudes like polarity, polarizabil-
ity, and linearity.
3
.6. 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 ther-
mograms on several heating and cooling cycles. In Fig. 7, compound C (series-1) shows
4
two endothermic peaks at 104.23°C and 146.92 °C in heating cycle, which designates the
Figure . DSC thermograms of compound (a) C (series-); (b) C (series-); (c) C (series-); (d) C (series-).





14
V. S. SHARMA ET AL.
−
− −
Table . Transition temperature (°C) and enthalpy (J g ) and entropy change (J g k ) by DSC
measurement.
Transition Heating scan(ºC) Cooling scan(ºC) ꢀH (−J g−) ꢀH (J g−
)
ꢀS (−J g−
k
−
)
ꢀS (J g
− −
k )
Comp.
C
Cr-SmC
.
.
>
.
.
>
.
.
>
.
>
.
.
—
.
.
—
.
.
—
.
.
.
.
.
.
.
.
.
.
.
.
.
—
.
.
—
.
.
—
.
.
.
.
.
.
.
.
.
.
.
.
.
—
.
.
—
.
.
—
(
series-) SmC–N
N-I
Cr-SmC
C
(
series-) SmC–N
N-I
Cr-SmC
C
(
series-) SmC–N
N-I
Cr-N
C
.
—
.
—
.
—
(series-) N-I
presence of SmC and nematic phase. That was further confirmed by POM analysis. While
on cooling condition, again two exothermic peaks were traced at 103.91°C and 145.41 °C.
Compound C12 (series-1) shows two endothermic peaks at 92.61°C and 126.32 °C during
heating cycle, while in cooling cycle, it appears at 93.67°C and 125.53 °C which was also
confirmed by POM analysis which indicates the mesophase looked in enantiotropical man-
ner. Compound C (series-2) exhibits two endothermic peak at 106.92 °C and 121.61 °C on
10
heating cycle which reveals with POM study. On cooling cycle, again two exothermic peaks
were traced at 105.98 °C and 122.67 °C. Compound C (series-2) shows only one significant
4
endothermic peak at 131.52°C in heating condition while it appears at 130.48 °C on cooling
condition. On POM study, it confirms the presence of nematic phase in heating and cooling
condition.
The phase transition temperatures and the value of enthalpy and entropy were measured
by carrying out DSC thermal analysis. The phase transition temperatures, enthalpy and
entropy values for the present synthesized series-1, -2 are summarized in Table 5. Molecules of
every homologue arbitrarily oriented in all likely directions with high order of disorder or
entropy (ꢀS = ꢀH/T) further than isotropic temperature and the enthalpy value (ꢀH). But,
at cooled condition, the matching from and lower isotropic temperature, the mesophase is
continued to seem reversibly at the lower temperature as observed during heating condition.
The mesophase attained in this present series is enantiotropically nematogenic.
4
. Conclusion
A new nonlinear homologous series of imine (schiff base, series-1) and ester (series-2) con-
taining ester and allylidene amino linking groups having left alkoxy side chains groups (n =
1
–8, 10, 12, 14, 16, 18) has been synthesized. The lower members C –C in both the series
1 3
showed nonliquid crystalline behavior while higher members of both the series exhibited
enantiotropic nematic or smectic phase transition with higher thermal stabilities.
Acknowledgments
Authors acknowledge thanks to Dr. R. R. Shah, principal and management of K. K. Shah Jarodwala
Maninagar Science College, Ahmedabad. Authors are also thankful to NFDD Centre for providing ana-
lytical and spectral services.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
15
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