Design and investigation of calamatic liquid crystals: Schiff base (?CH?N), chalcone (?CO?CH?CH?), and ester (?COO?) linkage group contain rigid rod shape with various terminal parts

Article abstract of DOI:10.1080/15421406.2016.1263115

The mesomorphic properties of linear schiff base-chalconyl ester homologous series can be designed in a predictable fashion with using various alcohol and para-tert-butyl phenol. We have synthesized total 14 novel liquid crystalline compounds and divided into two parts, i.e, series-1 (D₁ to D₁₀) and series-2 (E₁ to E₄). The result of both the series are compared and discussed. These compounds possess a rod-like geometry with rigid linear spacers and possessing smectic C and smectic A phases, while nematogenic phase was achieved by increasing the flexibility and broadening of tail-ended group in molecule. The texture image of mesophases is needle; rod like; broken fan type and nematic texture images are the type of schlieren and threaded in some homologue. All these compounds were characterized by elemental analyses and spectroscopic techniques such as FTIR and ¹H and ¹³C [NMR] spectroscopies. The mesomorphic properties of these compoundswere observed by optical polarized light microscopy and differential scanning calorimetry.

Full text of DOI:10.1080/15421406.2016.1263115

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Design and investigation of calamatic liquid
crystals: Schiff base (‒CH˭N), chalcone
(‒CO‒CH˭CH‒), and ester (‒COO‒) linkage group
contain rigid rod shape with various terminal parts
Vinay S. Sharma & R. B. Patel
To cite this article: Vinay S. Sharma & R. B. Patel (2017) Design and investigation of calamatic
liquid crystals: Schiff base (‒CH˭N), chalcone (‒CO‒CH˭CH‒), and ester (‒COO‒) linkage group
contain rigid rod shape with various terminal parts, Molecular Crystals and Liquid Crystals, 643:1,
141-158, DOI: 10.1080/15421406.2016.1263115
To link to this article: http://dx.doi.org/10.1080/15421406.2016.1263115
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Date: 26 February 2017, At: 09:02

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
http://dx.doi.org/./..
Design and investigation of calamatic liquid crystals: Schiff base
–
=
–
–
=
–
–
–
( CH N), chalcone ( CO CH CH ), and ester ( COO ) linkage
group contain rigid rod shape with various terminal parts
Vinay S. Sharma and R. B. Patel
Chemistry Department, K. K. Shah Jarodwala Maninagar Science College, Gujarat University, Ahmedabad,
Gujarat, India
ABSTRACT
KEYWORDS
Calamatic; enantiotropic;
liquid crystal; nematic;
smectic
The mesomorphic properties of linear schiff base-chalconyl ester
homologous series can be designed in a predictable fashion with using
various alcohol and para-tert-butyl phenol. We have synthesized total
14 novel liquid crystalline compounds and divided into two parts, i.e,
series-1 (D1 to D10) and series-2 (E1 to E4). The result of both the series are
compared and discussed. These compounds possess a rod-like geom-
etry with rigid linear spacers and possessing smectic C and smectic A
phases, while nematogenic phase was achieved by increasing the flex-
ibility and broadening of tail-ended group in molecule. The texture
image of mesophases is needle; rod like; broken fan type and nematic
texture images are the type of schlieren and threaded in some homo-
logue. All these compounds were characterized by elemental analy-
1
ses and spectroscopic techniques such as FTIR and H and 13C [NMR]
spectroscopies. The mesomorphic properties of these compounds were
observedbyopticalpolarizedlightmicroscopyanddifferentialscanning
calorimetry.
GRAPHICAL ABSTRACT
CONTACT Vinay S. Sharma
vinaysharma@gmail.com
Science College, Gujarat University, Ahmedabad , Gujarat, India.
Chemistry Department, K. K. Shah Jarodwala Maninagar
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gmcl.
©  Taylor & Francis Group, LLC

142
V. S. SHARMA AND R. B. PATEL
Introduction
Study of liquid crystalline state is a multidisciplinary subject and useful to mankind and vari-
ous industrial applications through scientist, technologists [1–4] due to its unique property to
flow as liquid and optical properties as crystals. Study on liquid crystal (LC) state is planned
with a view to understand and establish the effect of molecular structure on LC properties
[5, 6] as a consequence of molecular rigidity and flexibility [7,8]. In order to avail novel LC
materials to the various groups of researchers working by different aims, objects, and views
with different angles to continue and extend their research. Liquid crystals can be divided into
thermotropic, lyotropic, and metallotropic phases. Thermotropic and lyotropic liquid crystals
consist mostly of organic molecules although few minerals are also known [9]. Liquid crys-
tals in the nematic group are most widely used in production of liquid crystal displays mainly
due to their unique physical properties as well as wide range of temperature. In addition,
the nematic phase in which liquid crystal molecules are oriented on average along to a par-
ticular direction. By applying an electric or magnetic field, the orientation of the molecules
can be derived in a probable approach [10]. Literature survey revealed that the schiff base
has been widely employed as a linking group for the synthesis of different forms of liquid
crystals [11].
A number of chalcone having reported to exhibit a broad spectrum of antibacterial, anti-
fungal, antiulcer, antimalarial, antitumor, anticancer, anti-inflammatory, and antitubercular
activities [12–14]. It is believed that the presence of α, β-unsaturated functional group in
–
=
–
–
chalcone ( CH CH CO ) is responsible for antimicrobial activity, which can be altered
depending upon the type of substituent present on the aromatic rings [15,16]. To the best
of our knowledge, liquid crystalline materials based on chalconyl central linking group are
–
–
=
–
rarely reported in literature. It has been observed that CO CH CH linkage is less con-
ducive to mesomorphism as compared to CH N , COO , and N N linkages groups
because of the presence of nonlinearity and angle strain arising from the presence of keto
–
= – –
–
– =
– =
–
–
=
–
( C O) group [17]. Surprisingly, when CO CH CH linkage is linked with another link-
ing group it becomes conductive to induces mesomorphism. In the literature studies, there are
several reports of mesogenic compounds having chalcone linkage. Vora et al. [18] reported
a homologous series of polymers containing a chalcone linkage. Soon after words Chudghar
and his coworkers reported a homologous series containing on ester-chalcone linkages [19].
Yeap et al. have also synthesized mesomorphic compounds containing on ester-chalcone link-
age [20]. Patel et al. reported chalconyl-ester based two homologous series [21–22]. Guan
et al. reported phloroglucinol-based star-shaped symmetrical trimeric liquid crystalline com-
pounds containing three rod-like schiff base arms [23]. The mesomorphic properties of
aromatic Schiff base esters arising from substituents varying in their polarities have been
reported by Ha et al. [24]. Many mesogenic homologous series contain two central linkages,
one of which may be ester and the other azomethine [25,26]. Yellamaggad et al. reported in
2007 to synthesized six homologous series based on salicylaldimine-based banana-shaped
mesogens derived from laterally substituted resorcinol [27]. Recently, 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 [28–31].
Thus, the main object of this present work to synthesized and studied the effect of
chalconyl-ester linkage group containing schiff base and also geometrical shape on meso-
morphism. Many series of liquid crystalline compounds containing heterocyclic groups have
been synthesized due to their usefulness in wide application electrical, optical, biological, and

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
143
medical field [32]. In our previous reports, we have developed some homologous series based
on Cis-cinnamate and ester linkage group [33–35]. Recently, our research group reported
linear and nonlinear homologous series which consisted three phenyl rings bonded through
–
=
–
–
–
–
–
–
=
–
vinyl ester ( CH CH COO ) or ester ( COO ) and chalcone ( CO CH CH ) central
groups and varying left n-alkoxy terminal end group with different terminal group substi-
tuted on right tail group [36–40]. In continuation of efforts toward novel liquid crystalline
materials, we have introduce some new calamatic liquid crystal based on schiff base, chalcone
and terminally ester groups and also study the effect of broadening of molecule or increasing
the flexibility in mesogenic behavior.
Experimental
Materials
For present synthesized homologous series required materials: 4-hydroxy benzaldehyde, 4-
amino acetophenone purchased from S.R.L. Chemicals, Mumbai, 4-formyl benzoic acid was
purchased from Spectrochem, Mumbai, anhydrous K2CO3 was purchased from Finar Chem-
–
icals, India, N,N dimethyl amino pyridine and dicyclohexylcarbodiimide were purchased
from FlukaChemie, Switzerland. C16H33Br was purchased from S.R.L. Chemicals (Mumbai).
Propargyl alcohol and 4-tert-butyl phenol were purchased from Sigma Aldrich, different alco-
hols were purchased from Sigma Aldrich & S.R.L. Chemicals, Mumbai). The solvents were
dried and purified by standard method prior to use.
Measurements
Melting points were taken on Opti-Melt (automated melting point system). The FT-IR spec-
tra were recorded as KBr pellet on Shimadzu in the range of 3800–600 cm−1. Microanalysis
was performed on Perkin-Elmer PE 2400 CHN analyzer. The texture images were studied on
a trinocular optical polarizing microscope (POM) equipped with a heating plate and digital
camera. 1H NMR spectra and 13C NMR was recorded on a 400 MHz in Bruker Advance 400 in
the range of 0.5–16 ppm using CDCl3 solvent. The phase transition temperatures were mea-
sured using Shimadzu DSC-50 at heating and cooling rates of 10°C min−1. Texture image of
nematic phase were determined by miscibility method. Thermodynamic quantities enthalpy
(ꢀH) and entropy (ꢀS = ꢀH/T) are qualitatively discussed. For the POM measurement, the
newly synthesized compound is sandwiched between glass slide and cover slip and heating
and cooling rate is 2°C/min, respectively.
Synthesis
4-n-alkoxy hexadecyloxybenzaldehyde (A) was prepared by reported method [41]. 1-(4-((4-
(hexadecyloxy) benzylidene) amino) phenyl) ethanone (B) was prepared by usual estab-
lished method [42]. 4-(3-4((4-hexadecyloxy) benzylidene) amino) phenyl)-3-oxoprop-1en-
1-yl) benzoic acid (C) was prepared by reported method [43]. Esters D1 to D10 and E1 to E4
were synthesized by a method reported in literature [44]. Thus, the synthesized compounds
were filtered, washed with sodium bicarbonate solution, dried and purified till constant tran-
sition temperatures is obtain, using an POM equipped with a heating stage. The synthetic
route to a series is mentioned in Schemes 1 and 2.

144
V. S. SHARMA AND R. B. PATEL
Scheme . Synthesis route of series  (D to D).
Synthesis of -n-hexadecyloxy benzaldehyde (A)
4-n-Hexyloxy benzaldehyde (A) was synthesized by refluxing the mixture of 4-hydroxy ben-
zaldehyde (1 equiv.) with corresponding n-hexadecyl bromide (C16H33Br) (1 equiv.) in pres-
ence of anhydrous K2CO3 (1 equiv.) in dry acetone as a solvent [41].
Synthesis of -(-((-hexadecyloxy) benzylidene) amino) phenyl) ethanone (B)
1-(4-((4-(hexadecyloxy) benzylidene) amino) phenyl) ethanone was prepared by refluxing
the mixture of (B) and 4-amino acetophenone 3–4 hr in presence of ethanol and few drops of
acetic acid [42]. The resultant mixture was filtered, dried, and purified by column chromatog-
raphy which was confirmed by IR and 1H NMR analysis.
Synthesis of -(-((-hexadecyloxy) benzylidene) amino) phenyl)--oxoprop--en--yl)
benzoic acid (Chalcone) (C)
4-(3-4((4-hexadecyloxy) benzylidene) amino) phenyl)-3-oxoprop-1en-1-yl) benzoic acid (C)
was prepared by usual established method reported in literature [43].

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
145
Scheme . Synthesis route of compound E to E.
Synthesis of ester derivatives (D to D and E to E)
The compound has been prepared by esterification of the appropriate (A) (2.02 mmol) and
chalcone (C) (0.246 g, 2.02 mmol), dicyclohexylcarbodiimide (DCC) (0.457 g, 2.22 mmol)
and dimethylaminopyridine (DMAP) in catalytic amount (0.002 g, 0.2 mmol) in dry CH2Cl2
(DCM) (50 mL) was stirred at room temperature for 48 hr. The white precipitate of DCU is
obtained which was isolated by filtration and discarded, while the filtrate was evaporated to
dry. The resultant crude product was purified by column chromatography on silica gel eluting
with dichloromethane:methanol and recrystallization from methanol:chloroform (2:4) until
the constant transition temperatures were observed [44].
Analytical data
−1
– – –
–
Compound (C): FT-IR (KBr) in cm : 3030 ( C H str in aromatic), 2858–2932 (C H str
CH3), 1365 and 1219 ( C O str), 960 (trans, CH CH in CO CH CH group), 802 dis-
ubstituted aromatic ring (para), 681 polymethylene ( CH2 ) of OC16H33(n), 1641 ( CH N,
str. azomethine group), 1660 ( C O str. carbonyl), 2550 ( OH of COOH group). H NMR:
– –
–
=
–
–
=
–
–
–
–
–
–
=
1
– =
–

146
V. S. SHARMA AND R. B. PATEL
–
–
–
–
δH (CDCl3, 400 MHz): 0.88–0.89 (t, 3H, CH3 of OC16H33 group), 1.29–1.24 (m, 8H, -
–
–
–
(CH2)4), 1.26–1.25 (m, 14H, -(CH2)7), 1.76 (t, 3H, CH2 ), 4.03–4.06 (t, 3H, OCH2 ),
7.04 (d, 1H, α, CO CH CH ), 8.29 (d, 1H, β, CO CH CH ), 7.06–7.82 (4H, first
phenyl ring), 7.41–7.86 (4H, second phenyl ring), 7.57–7.81 (4H, third phenyl ring), 10.8–
11.0 (1H, OH in COOH group); C NMR (CDCl3): δ ppm 13.9 ( CH3 of OC16H33
chain), 22.71–29.5, 30.8, ( CH2 aliphatic), 64.1 ( OCH2), 114.12, 129.83, 122.80, 134.22,
129.44, 130.71, 128.02 (Ar C), 120.24 (α carbon of CO CH CH), 144.92 (β carbon of
CO CH CH), 186.42 (C O group of chalcone). Elemental analysis of C39H49NO4: calcu-
lated: C; 67.60%, H; 5.91%, O; 22.53%, N; 3.94%, found: C; 67.52%, H; 5.43%, O; 21.70%, N;
3.90%.
–
–
=
–
–
=
–
13
–
–
–
–
–
–
=
–
–
–
–
=
–
=
–
–
–
– – –
Compound (E3): FT-IR (KBr): 630 polymethylene ( CH2 )n of OC16H33, 920 ( C H
– – –
– – –
–
def. hydrocarbon), 1028 and 1068 ( C O ) str, 1427 ( C H def. in CH2), 1514
– = – – =
–
=
( C C ) str, 1602 ( CH N of azomethine), 1658 ( C O group in chalcone), 1740
–
–
–
– –
–
=
–
( COO ester group), 2840 and 2960 ( C H str in CH3), 930 (trans, CH CH in
CH CH CO group), 2260 (alkyne group),1H NMR (CDCl3): δ ppm 0.88–0.90 (t,
=
–
–
–
–
–
–
3H, CH3 of OC16H33), 1.26–1.44 (m, 26H, CH2 of OC16H33), 1.76 (t, 2H of
–
– –
–
–
–
OC16H33), 3.32 (1H, terminal alkyne group), 4.02–4.06 (t, 2H, O CH2 of OC16H33),
–
–
=
–
–
=
–
7.52 (d, 1H, J = 15.1 Hz, CO CH CH ), 8.28 (d, 1H, J = 15.1 Hz, CO CH CH ),
7.04–7.82 (d, 4H, left side phenyl ring), 7.40–7.88 (d, 4H, central phenyl ring), 7.47–
7.63 (d, 4H, terminal phenyl ring). Elemental analysis of C42H51NO4: calculated: C;
79.62%, H; 8.05%, O; 10.11 %, N; 2.21%, found: C; 79.58%, H; 7.98 %, O; 10.02%, N;
2.13%.
–
–
–
– – –
Compound (E4): FT-IR (KBr): 636 polymethylene ( CH2 )n of OC16H33, 839 ( C H
– – – – – –
def. disubstituted para), 952 ( C H def. hydrocarbon), 1028 and 1068 ( C O ) str, 1197 and
– –
–
=
1228 ( C O str in -(CH2)n chain, 1575–1515 (C=C aromatic ring stretching), 1602 ( CH N
–
=
–
– =
–
–
of azomethine), 930 (trans, CH CH ) str, 1670 ( C O group), 1726 ( COO ester group),
1
– –
–
2860 and 2970 ( C H str in CH3). H NMR (CDCl3): δ ppm 0.88–0.90 (t, 3H, CH3 of
OC16H33), 1.26–1.44 (m, 26H, CH2 of OC16H33), 1.28–1.29 (m, 8H, CH2 of OC16H33),
1.34 (s, 9H, -(CH3)3), 1.76 (t, 2H of OC16H33), 4.02–4.06 (t, 2H, O CH2 of OC16H33),
7.52 (d, 1H, J = 15.1 Hz, CO CH CH ), 8.28 (d, 1H, J = 15.1 Hz, CO CH CH ), 7.04–
7.82 (d, 4H, left side phenyl ring), 7.40–7.88 (d, 4H, central phenyl ring), 7.47–7.63 (d, 4H,
third phenyl ring), 7.28–7.65 (d, 4H, last phenyl ring). Elemental analysis of C49H61NO4: cal-
culated: C; 80.80%, H; 8.39%, O; 8.80%, N; 1.92%, found: C; 79.31%, H; 8.31%, O; 8.73%, N;
1.82%.
Compound (E2): FT-IR (KBr): 648 polymethylene ( CH2 )n of OC16H33, 841 ( C H
def. disubstituted para, 951 (trans, CH CH ), 1028 and 1068 ( C O ) str, 1602 ( CH N
–
–
–
–
–
–
–
– –
–
–
–
=
–
–
–
=
–
–
–
–
– – –
–
=
–
– – –
–
=
– = –
– =
–
–
of azomethine), 1514 ( C C ) str, 1666 ( C O group), 1726 ( COO ester group), 2850
1
– –
–
–
and 2970 ( C H str in CH3). H NMR (CDCl3): δ ppm 0.88 (t, 3H, CH3 of OC16H33), 0.91
–
–
–
–
–
(d, 6H, CH2 CH (CH3)2), 1.24–1.43 (m, 26H, CH2 of OC16H33), 1.28–1.29 (m, 8H, CH2
of OC16H33), 1.73 (t, 2H of OC16H33), 4.02–4.06 (t, 2H, O CH2 of OC16H33), 7.51 (d,
1H, J = 15.1 Hz, CO CH CH ), 8.24 (d, 1H, J = 15.1 Hz, CO CH CH ), 7.04–7.81 (d,
4H, left side phenyl ring), 7.40–7.87 (d, 4H, central phenyl ring), 7.47–7.63 d, 4H, third phenyl
ring). Elemental analysis of C43H57NO4: calculated: C; 79.26%, H; 8.75%, O; 9.83%, N; 2.15%,
found: C; 79.18%, H; 8.40%, O; 9.69%, N; 2.08%.
–
–
– –
–
–
–
–
=
–
–
–
=
–
–
–
–
–
– – –
Compound (D12): FT-IR (KBr): 638 polymethylene ( CH2 )n of OC16H33, 839 ( C H
–
–
def. disubstituted para), 701 polymethylene ( CH2 ) of C12H25 with terminal ester group,
– – – – – –
–
=
–
952 ( C H def. hydrocarbon), 930 (trans, CH CH ), 1068 ( C O ) str, 1197 and 1228
– – – =
–
=
– = –
( C O str) in -(CH2)n chain, 1602 ( CH N of azomethine), 1514 ( C C ) str, 1660 ( C O

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
147
Table . Nematic phase of compounds D, D, D, D, E, and E by miscibility method.
Sr. No.
Homologue
Texture

D
D
D
D
E
Rod like nematic
Droplets
Threaded
Schlieren
Schlieren





E
Mosaic nematic
1
–
–
– –
group), 1760 ( COO ester group), 2850 and 2970 ( C H str in CH3). H NMR (CDCl3): δ
–
–
–
–
–
ppm 0.88–0.90 (t, 6H, CH3 of C12H25 and OC16H33), 1.32 (q, 4H, CH2 of C12H25 and
OC16H33), 1.26–1.28 (m, 20H, CH2- of C12H25 and OC16H33), 1.29 (m, 16H, C12H25
and OC16H33), 1.76 (t, 2H of OC16H33 group), 1.80 (t, 2H of C12H25 group), 4.02–4.06 (t,
–
–
–
–
–
–
–
–
– –
–
–
–
–
=
–
–
=
–
6H, O CH2 CH2 of OC16H33 and C12H25), 7.54 (d, 1H, J = 15.1 Hz, CO CH CH ),
–
–
–
8.06–8.08 (d, 1H, J = 15.1 Hz, CO CH CH ), 7.04–7.82 (d, 4H, left side phenyl ring), 7.40–
7.84 (d, 4H, central phenyl ring), 7.46–7.61 (d, 4H, terminal phenyl ring). Elemental analysis
of C51H73NO4: calculated: C; 80.20%, H; 9.56%, O; 8.38%, N; 1.83%, found: C; 79.08%, H;
9.30%, O; 8.32%, N; 1.78%.
–
–
–
–
– – –
Compound (D10): FT-IR (KBr): 637 polymethylene ( CH2 )n of OC16H33, 839 ( C H
–
–
– – –
def. disubstituted para), 821 polymethylene ( CH2 ) of C10H21, 952 ( C H def. hydrocar-
–
– –
=
–
–
=
– – –
bon), 930 (trans, CH CH ), 1610 ( CH N of azomethine), 1028 and 1068 ( C O ) str,
– = –
– =
1197 and 1228 ( C O str in -(CH2)n chain, 1514 ( C C ) str, 1640 ( C O group), 1760
1
–
–
– –
( COO ester group), 2850 and 2970 ( C H str in CH3). H NMR (CDCl3): δ ppm 0.88–
–
–
–
–
–
–
0.89 (t, 6H, CH3 of C10H21 and OC16H33), 1.32 (q, 4H, CH2 of C10H21 and OC16H33),
1.26–1.28 (m, 16H, CH2 of C10H21 and OC16H33), 1.29 (m, 16H, CH2 of C10H21 and
OC16H33), 1.73 (t, 2H of OC16H33 group), 1.80 (t, 2H of OC10H21 group), 4.02–4.06 (t,
–
–
–
–
–
–
–
–
–
–
– –
–
–
–
–
=
–
–
=
–
6H, O CH2 CH2 of OC16H33 and C10H21), 7.53 (d, 1H, J = 15.1 Hz, CO CH CH ),
–
–
–
8.04–8.08 (d, 1H, J = 15.1 Hz, CO CH CH ), 7.05–7.83 (d, 4H, left side phenyl ring), 7.40–
7.84 (d, 4H, central phenyl ring), 7.46–7.61 (d, 4H, terminal phenyl ring). Elemental analysis
of C49H69NO4: calculated: C; 80.00%, H; 9.38%, O; 8.70%, N; 1.30%, found: C; 79.10%, H;
9.30%, O; 8.62%, N; 1.22%.
–
–
–
– – –
Compound (D5): FT-IR (KBr): 656 polymethylene ( CH2 )n of OC16H33, 839( C H
–
–
–
–
=
def. disubstituted para), 759 polymethylene ( CH2 ) of C5H11, 1610 ( CH N of azome-
– – – – – –
–
=
–
thine), 951 ( C H def. hydrocarbon), 960 (trans, CH CH ), 1028 and 1068 ( C O ) str,
– –
–
– = –
– =
1197 and 1228 ( C O str.) in ( CH2)n chain, 1540 ( C C ) str, 1630 ( C O group), 173
( COO ester group), 2850 and 2977 ( C H str in CH3). H NMR (CDCl3): δ ppm 0.88–0.90
(t, 6H, CH3 of C5H11 and OC16H33), 1.31 (q, 4H, CH2 of C5H11 and OC16H33), 1.26–
1.28 (m, 20H, CH2 of C5H11 and OC16H33), 1.29 (m, 6H, C5H11 and OC16H33), 1.75
1
–
–
– –
–
–
–
–
–
–
–
–
–
–
–
–
–
–
– –
–
–
(t, 2H of OC16H33 group), 1.80 (t, 2H of C5H11 group), 4.02–4.06 (t, 6H, O CH2 CH2 of
–
–
–
–
=
–
OC16H33 and C5H11), 7.52 (d, 1H, J = 15.1 Hz, CO CH CH ), 8.04–8.08 (d, 1H, J =
–
–
=
–
15.1 Hz, CO CH CH ), 7.04–7.83 (d, 4H, left side phenyl ring), 7.40–7.86 (d, 4H, central
phenyl ring), 7.46–7.61 (d, 4H, terminal phenyl ring). Elemental analysis of C44H53NO4: cal-
culated: C; 80.12%, H; 8.04%, O; 9.71%, N; 2.12%, found: C; 79.96%, H; 8.98%, O; 9.68%, N;
2.08%.
Textures of nematic phase were determined by miscibility method, which were mention in
Table 1. D7 homologue shows rod-like nematic mesophase, D8 shows droplets-type nematic
mesophase, D12 and E2 show schlieren-type of nematic mesophase, D10 homologue shows

148
V. S. SHARMA AND R. B. PATEL
Table . Transition temperature of series-D in °C by POM.
Transition temperatures in °C
SmA Nm
Sr. No.
R = n-alkyl group
Cr
SmC
Iso










D
D
D
D
D
D
D
D
D
D
·
·
·
·
·
·
·
·
·
·
.
.
.
.
.
.
.
.
.
.
—
—
—
—
—
·
—
—
—
.
.
.
—
—
—
—
—
—
—
—
·
—
—
—
—
—
·
·
·
·
·
·
·
·
·
·
.
.
.
.
.
.
.
.
.
.
·
·
·
·
·
·
·
·
·
·
·
—
·
·
.
.
.
.
·
·
·
·
·
·
Cr = solid crystal, SmC = smectic C phase, SmA = smectic A phase, Nm = nematic phase, Iso = isotropic phase.
threaded-type nematic phase, and E3 homologue display mosaic-type nematic mesophase.
Transition temperatures of series-1 (D1 to D10) and series-2 (E1 to E4) are shown in Tables 2
and 3, respectively.
Result and discussion
Here in, we have synthesized newly calamatic rod-like homologous series based on three link-
ing groups and hexadecyloxy side chain present in left side while right terminal part is vary-
ing. In the present investigation, we study the effect of linkage group and varying flexibility on
mesomorphism. The phase behavior of all new synthesized compounds has been investigated
by POM and confirm by using differential scanning calorimetry (DSC) analysis.
DSC analysis
DSC is a valuable method for the detection of phase transitions. The thermal behavior of novel
homologues series were confirmed by using DSC measurement shown in Figs. 1 and 2. The
transition temperatures and associated with enthalpychanges determined by DSC for com-
pounds are mentioned in Table 1. DSC thermogram is traces in heating and cooling condi-
tions. D4 homologue shows first endothermic peak at 131.15°C, which indicates the presence
of Cr-SmC mesophase. While second endothermic peak traces at 148.25°C, which indicates
the presence of SmC-SmA mesophase. Applying further heating, it is isotropic at >160°C.
On cooling condition, one endothermic peak was trace at 139.12°C which indicate the pres-
ence of SmA phase enantiotropically. Compound D5 shows two significant peaks in both
heating and cooling conditions, it observed at 122.21°C and 138.02°C and on cooled condi-
tion it traced at 142.12°C and 121.04°C. The SmA phase transform into isotropic at >150°C,
which was further confirmed by POM investigation. For E1 homologue, first endothermic
Table . Transition temperature of E to E in °C by POM.
Transition temperatures in °C
Sr. No.
R = n-alkyl group
Cr
SmC
SmA
Nm
Iso

E
E
E
E
·
·
·
·
.
·
·
·
·
—
—
—
—
·
·
·
·
.
.
.
.
·
·
·
·
.
.
.
.
·
·
·
·



.
.
.
Cr = Solid Crystal, SmC = Smectic C phase, SmA = Smectic A phase, Nm = Nematic phase, Iso = Isotropic phase.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
149
Figure . DSC thermogram of compounds D, D, E, and E.
peak trace at 131.02°C, which shows the presence of SmC phase, and second endothermic
peak trace at 148.21°C, specifies the presence of nematic phase in heating condition and trans-
ferred into isotropic at >178°C. On cooling condition again two peak traces at 122.43°C and
151.41°C indicating the mesophase appeared enantiotropically manner. E3 homologue traces
two significant endothermic peaks at 85.61°C and 144.57°C and transform into isotropic
from nematic at >180°C, while, on cooling condition, again two peaks traces at 92.11°C and
145.56°C, respectively. Transition temperature obtained by DSC analysis at heating and cool-
ing condition and the value of enthalpy and entropy is shown in Table 4. The value of enthalpy
Figure . DSC thermogram of compounds D, D, D, and D.

150
V. S. SHARMA AND R. B. PATEL
Table . Phase transition temperature (°C) and enthalpy (J g−) and entropy change (J g−k−) by DSC
measurement.
Heating peak Cooling peak
temperature temperature
microscopic microscopic
temperature temperature
Compound
Transition
Cr-SmC
SmC-SmA
SmA-I
Cr-SmC
SmC-SmA
SmA-I
(°C)
(°C)
ꢀH (-Jg−
)
ꢀH (Jg−
)
ꢀS (J g−k−) ꢀS (J g−k−
)
D
D
.
.
>
.
.
>
.
.
>
.
—
.
—
.
.
—
.
.
—
.
.
—
.
.
.
.
.
.
.
.
.
.
.
.
—
.
—
.
.
—
.
.
—
.
.
—
.
.
.
.
.
.
.
.
.
.
.
.
—
.
—
.
.
—
.
.
—
.
.
—
E
Cr-SmC
SmC-N
–
E
N I
Cr-SmC
SmC-N
.
>
–
N I
and entropy of compound D7, D8, D10, and D12 are mention in Table S1 (see supporting infor-
mation). The liquid crystalline phases are obtained an enantiotropically manner in present
synthesized series (D1 to D10 and E1 to E4).
The higher homologous (D7 to D12) displayed enantiotropic smectic C (SmC) as well as
nematic mesophase and on cooling condition two peaks were trace and confirm the pres-
–
ence of SmC and nematic phase. We observe that N I transition occur in higher homologue
due the flexibility increase by tail-ended group inbuilt with ester linkage and further con-
firm by POM analysis. Investigation of phase sequence by DSC analysis is further confirmed
by POM investigation. Figure 3 shows mesophase appear in heating and cooling conditions,
respectively.
POM investigation
The targeted calamatic rod-like liquid crystalline compounds were synthesized by the reaction
of 4-(3-4((4-hexadecyloxy) benzylidene) amino) phenyl)-3-oxoprop-1-en-1-yl)benzoic acid
with various linear and nonlinear alcohol and 4-tert butyl phenol. In present study, we have
synthesized total fourteen homologue (D1 to D10 and E1 to E4) in which D1 to D3 shows SmC
Figure . Phase sequence of D homologue by DSC analysis.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
151
Figure . Phase behavior of series- (D to D).
phase, while D4 to D6 displayed SmC and SmA phase and rest of homologues D7 to D10 exhib-
ited SmC and nematic mesophase enantiotropically manner except D4 homologue. The tran-
sition temperatures of newly synthesized compounds were determined by polarization optical
microscope is mentioned in Tables 2 and 3. The phase diagram were plotted against transi-
tion temperature versus the number of carbon atoms present in n-alkyl chain in terminal end
–
group ( OR) is shown in Figs. 4 and 5, respectively. The phase diagram shows Cr-SmC, SmC-
–
SmA, SmC/SmA/N I transition curves drawn by linking the transition temperatures points.
Cr-SmC transition curve initially falling as series is increased with number of methylene unit
linked in it and slightly increased at D6 and then continued to descend up to D12 homologue.
Nematic phase commences from D7 in D1 to D10. The SmC-N transition curve starts rising
from D7 homologue and reaching maxima at D8 due to abnormality effect and then descends
–
up to last homologue. Odd-even effect is present in SmC-N and SmC/SmA/N I transition
curves. SmC-SmA transition curve descend from D4 to D6 homologue, this is because of
–
–
increasing the number of methylene unit CH2 in right terminal group which increases its
–
chain length and causes more flexibility. SmC/SmA/N I curve falling initially at D7 and then
rising to C8 and descends at C10 and again rising at C12 homologue. The mesogenic properties
are varying from homologue to homologue in same series because of added methylene group
Figure . Phase behavior of compound (E to E).

152
V. S. SHARMA AND R. B. PATEL
Figure . Optical micrographs of (a) broken fan type texture in SmC phase at °C of compound D, (b)
SmA phase at °C of compound D, (c) SmC phase at °C of compound D and (d) broken fan type SmC
phase at °C of compound E. (Cross polarizer).
with ester linkage at terminal side. The common structural features associated with all these
compounds are that they consist three linkage groups and varying only right terminal part.
Figure 5 indicates the phase diagram of compounds E1 to E4. Homologue E1 and E2
contained isopropyl- and isobutyl-tailed groups while in E3 homologue propargyl group
present at tail ended side. However, in E4 homologue paratert butyl phenyl group is present.
Cr-SmC transition curve starts falling from E1 to E3 homologous and then increased
at E4 homologue because of widening of molecular chain length and also presence one
more benzene core as compared to E1 to E3 homologous, respectively. SmC-N transition
–
curve gradually starts increase from E1 to E4 homologue. N I transition curve is start
falling from E1 to E4 homologue and then increased at E3 homologue and descend at E4
homologue.
Under the polarizing microscope, a broken focal conic texture as typical for SmC phase was
observed upon heating of compound D3 from the solid phase. Optical texture was observed
for compound D3 at 138°C given in Fig. 6(a). A typical texture for SmA phase was observed
for compounds D6. The texture observed at 122°C mention in Fig. 6(b). A needle-type image
of SmC phase was observed for compound D7 at 111°C shown in Fig. 6(c). A broken fan-type
texture image of SmC phase was observed for compound E3 at 83°C given in Fig. 6(d). No
other mesophase transition, except crystallization, was realized on further cooling of com-
pound up to room temperature. All the transition temperatures observed under POM agreed
with DSC data.
Figure 7 indicates the POM image of compound D10, D12, D5, and E2 homologous,
POM observation reveal that upon heating from the crystal state compound to isotropic

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
153
Figure . Optical micrographs of (a) rod type texture image in nematic phase at °C of compound D, (b)
SmC phase at °C of compound D, (c) SmA phase at °C of compound D, and (d) mosaic type SmC
phase at °C of compound E. (Cross polarizer).
temperature. Compound D10 shows rod-type image of nematic mesophase at 110°C. Com-
pound D12 exhibits SmC mesophase at 74°C while in compound D5, the molecules are aligned
parallel to the layer and maintaining long-range orientational ordering and short-range posi-
tional ordering which lead to the SmA mesophase. Compound E2 shows mosaic type of SmC
mesophase at 132°C.
The mesophase exist enenatiotropically in present synthesized compounds. Compound
D4 shows mesophase in heating and cooling conditions. Figure 8 indicates the presence of
smectic mesophase in D4 homologue at 130°C in cooling condition.
We have measured the phase sequence of D4 homologue on cooling condition depicted
in Fig. 9, which was confirm by DSC analysis discussed in Fig. 3. (a) Isotropic at 160°C
Figure . SmA phase at °C in D homologue.

154
V. S. SHARMA AND R. B. PATEL
Figure . Phase sequence of D homologue on cooling condition by POM study.
while applying cooling below than 150°C, mosaic type of SmA mesophase is exhibited, (b)
commencement of SmA mesophase at 144°C, (c) mosaic-type texture image is observed at
142°C, (d) applying further cooling up to 130°C, SmA phase is transform into SmC phase,
and (e) decreasing on cooling rate finally solid crystal is generate, which cannot be seen
in given POM image. Observed phase sequence is also been seen in heating condition,
respectively.
Thermal stability of mesophase
Some LC parameters evaluated from thermotropic data of novel synthesized series-1 and its
compare with compounds E2 and E4 homologues, respectively. The presence of three link-
age groups is similar in all synthesized compounds. However, they differ with only termi-
nal end part. Therefore, the molecular rigidity and right-side flexibility is changing due to
–
variation in chain length but at left-side hexadecyloxy chain ( OC16H33) is common in all
synthesized compounds. The molecular rigidity is unaltered in series-1 while its changing
in compound E1 to E2 because of presence of nonlinear carbon chain. Whereas E3 homo-
logue consists linear propyne side chain linked with ester group at terminal part, which dif-
fer its molecular rigidity as well as linearity. Compound E4 has one more terminal benzene
core unit with tert butyl group which differ it from other synthesized compounds shown in
Fig. 10.
–
–
The changing fashion in thermometric data is ascribed to the successive addition of CH2
unit at terminal end side in series-1. Added methylene units or units that increase its molec-
ular length, permanent dipolement, dispersion forces, molecular polarity and polarizability,
rigidity and flexibility across the molecular axis with changing the value of enthalpy (ꢀH)
–
and keeping rest of the molecular part including left-side tail group OC16H33 and three
linking groups intact throughout the series. Consequently, variation occurs in intermolecular

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
155
Figure . Structurally similar series- and compounds E and E.
adhesion forces of suitable magnitudes that induce nematic mesophase in higher homologues
like D7 to D12 in series-1. Broadening of molecular due to presence of nonlinear substituted
at terminal side exhibiting smectic C as well as nematic mesophase enantiotropically manner.
Table 4 shows the average thermal stabilities and mesophase range of series I (D1 to D10)
–
compare with E1 to E4 homologous. The N I thermal stabilities of series I and compound
E1 to E4 are 119.5°C and 147°C. The SmC-SmA and SmA-I thermal stabilities of series-1 are
133.2°C and 136°C. Thermal stabilities of SmC-N phase of series I and compound E1 to E4
are 94.75°C and 115°C, while SmC-I thermal stability of series-1 is 118.4°C. From the Table 5,
it can be seen that the average mesophase length of (Sm + N) phase of series I is 24.0°C and
64.0°C and average mesophase length of (Sm + N) phase of compound E1 to E4 is 43.0°C
–
and 96.0°C, respectively. Thermal stability of SmC-N and N I phase of compound E1 to E4 is
higher than series-1.
The space-filling diagram suggests the energy minimize in series-1 (D1) and series
(E2, E4) homologous shown in below Fig. 11. The geometrical shape of series-1 is rod type as
–
=
–
–
compared to E3 and E4 homologues. Presence of trans ethylene ( CH CH ) group in chal-
–
–
=
–
–
=
–
cone linkage ( CO CH CH ) with azomethine ( CH N) and carboxy ( COO ) linking
group is common in all synthesized compounds. In E3 homologue, nonlinear chain ( C4H9),
–
which disturb the linearity of molecule and presence of tert butyl group on fourth phenyl
group attach with third phenyl ring in E4 homologue. Thus, the length of E4 homologue is
higher than other 14 synthesized homologues in present series. Linking group is one of the
factors to exhibiting the smectic phase instead of a nematic phase in synthesized target com-
pounds. The ester linking group favor the lamellar packing due to the dipole-dipole interac-
tion which ultimately generated the smectic phase [45].
Table . Average thermal and mesophase stabilities of series- and compound E to E in °C.
Series
Series- (D to D)
Compound E to E
SmC-SmA
.
.

—
.
—
–
N I
SmA-I
SmC-N
SmC-I
.
.
.–.
D, D
D

—
.–.
E, E
E
Total mesophase length
(Sm + N)
Commencement of smectic phase
Commencement of nematic phase
D
E

156
V. S. SHARMA AND R. B. PATEL
Figure . Space-filling diagram of compounds (a) D, (b) E, and (c) E.
Photophysical behavior
The preliminary studies of the photochemical properties were carried out on E3, E4, and D5
compounds in the chloroform solution (c = 1.5 × 10−5 mol/l−1). The UV-vis absorption
spectra of all calamatic-shaped compounds displayed primarily two absorptions with max-
imum absorbance at about 350, 350, and 355 nm mentioned in Fig. 12. The absorption spec-
tra are probably identical for two compounds E3 and D5 due to same molecular structure,
with variation in only terminal side methylene group. However, in compound E4 maximum
absorption spectra as is at 355 nm due to presence of paratert butyl phenyl ester which is
higher than other. Therefore, we have introduced only compound, D5 from series-1, for the
study of photoisomerization.
Figure . UV/Vis absorption spectra of (E, E, and D) in chloroform, c = . × − mol/l−.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
157
Conclusion
We synthesized 14 calamatic liquid crystals based on schiff base, chalcone and ester link-
ing group. Three rod-shaped monomers containing three linkage groups derived from linear,
nonlinear alcohol, and paratert butyl phenol as tail units were synthesized. The LCs behavior
of newly synthesized compounds was measured by POM study and confirm by DSC analysis.
The photophysical behavior of synthesized compound measured by UV/Vis analysis. D1 to D3
compound shows SmC phase, while D4 to D6 shows SmC to SmA mesophase, and rest of the
homologous displayed SmC as well as nematic phase. The group efficiency order derived on
the basis of thermal stability, early commencement of mesophase, upper and lower mesophase
lengths.
Acknowledgments
Authors acknowledge thanks to Dr. R. R. Shah, principal of K. K. Shah Jarodwala Maninagar Science
College, Ahmedabad. Author also gratefully thanks to Anuj S. Sharma (Chemistry department, Gujarat
University) and Akshara. P. Shah (Chemistry department, Mumbai University) for giving fruitful dis-
cussions in DSC and UV analysis.
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