Synthesis and mesomorphic properties of quinoline-8-yl-4-((4-n-alkoxy benzylidene) amino) benzoate: The effect of linkage group

Article abstract of DOI:10.1080/15421406.2017.1358006

A new homologous series viz. quinoline-8-yl-4-((4-n-alkoxy benzylidene) amino) benzoate based on two central linking groups have been designed and characterised by elemental analyses and spectroscopic techniques such as Fourier transform infrared [FT-IR] and protonmagnetic resonance magnetic resonance [1H NMR] spectroscopy. The mesomorphic properties of these compounds were observed by polarizing optical light microscopy (POM) and confirmed by differential scanning calorimetry (DSC). All synthesized compounds displayed LC property except first two homologue. The lower homologues (n = 4 to 8) display SmA and SmC phase while, in higher homologues (n = 10 to 18) SmC and nematic phasewere seen in heating and cooling condition.

Full text of DOI:10.1080/15421406.2017.1358006

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Synthesis and mesomorphic properties of
quinoline-8-yl-4-((4-n-alkoxy benzylidene) amino)
benzoate: The effect of linkage group
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): Synthesis and mesomorphic properties of quinoline-8-yl-4-((4-n-alkoxy benzylidene)
amino) benzoate: The effect of linkage group, Molecular Crystals and Liquid Crystals, DOI:
10.1080/15421406.2017.1358006
To link to this article: http://dx.doi.org/10.1080/15421406.2017.1358006
Published online: 12 Sep 2017.
Submit your article to this journal
Article views: 7
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
http://www.tandfonline.com/action/journalInformation?journalCode=gmcl20
Download by: [Imperial College London Library]
Date: 14 September 2017, At: 03:46

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
https://doi.org/./..
Synthesis and mesomorphic properties of quinoline--yl--
((-n-alkoxy benzylidene) amino) benzoate: The effect
of linkage group
Vinay. S. Sharmaa, Rajesh H. Vekariyab, Anuj. S. Sharmab, and R. B. Patela
aChemistry Department, K.K. Shah Jarodwala Maninagar Science College, Gujarat University, Ahmedabad,
Gujarat, India; bDepartment of Chemistry, School of Science, Gujarat University, Ahmedabad, Gujarat India
ABSTRACT
KEYWORDS
Mesomorphic; nematic;
smectic; thermotropic
A new homologous series viz. quinoline-8-yl-4-((4-n-alkoxy benzyli-
dene) amino) benzoate based on two central linking groups have been
designed and characterised by elemental analyses and spectroscopic
techniques such as Fourier transform infrared [FT-IR] and proton-
magnetic resonance magnetic resonance [1H NMR] spectroscopy.
The mesomorphic properties of these compounds were observed by
polarizing optical light microscopy (POM) and confirmed by differential
scanning calorimetry (DSC). All synthesized compounds displayed LC
property except first two homologue. The lower homologues (n = 4 to
8) display SmA and SmC phase while, in higher homologues (n = 10 to
18) SmC and nematic phase were seen in heating and cooling condition.
GRAPHICAL ABSTRACT
1. Introduction
Suitable magnitudes of anisotropic forces of intermolecular attractions as a consequence
of molecular rigidity and flexibility can favorably induce a physically distinct state of a
substance between the crystalline solid and the isotropic liquid states, called the liquid crystal
state [1–3]. Normally structures consist of two or more rings (aromatic, homocyclic or
CONTACT Vinay. S. Sharma
Science College, Gujarat University, Ahmedabad, Gujarat, , India; Rajesh H. Vekariya
vinaysharma@gmail.com
Chemistry Department, K.K. Shah Jarodwala Maninagar
rajeshvekariya@gmail.com
Department of Chemistry, School of Science, 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

2
V. S. SHARMA ET AL.
heterocyclic) and central linking part encompass the rigidity and presence of terminal groups
act as the flexible part of the molecule. The introduction of aromatic groups such as biphenyl
or naphthyl ring has been widely studied because they give rise to very stable mesophases
and allow the introduction of substituents into different positions leading to modification of
the liquid crystalline property [4–5].
In the last few years, heterocyclic liquid crystals have been of great scientific interest. The
presences of heterocyclic as a part of the core provide perpendicular dipolar moments as well
as polarizable structures, which can lead to SmC phases [6]. 2, 6-disubstituted quinoline based
liquid crystalline compounds were synthesized and their mesogenic properties were reported
in literature [7–9]. Lin et al. reported first heterocyclic liquid crystalline molecules containing
3,7-disubstituted quinoline displayed widest range of SmC phase [10]. Zanardi et al. reported
2-phenylquinolines with alkyl or alkoxyl substituents in positions at 6 and 4ꢀ side which dis-
played nematic mesophase [11]. Previously, Chia et al. reported a regioselective addition of
organometallic reagents to 1-acylpyridinium and 1-acylquinolinium salts to prepare nitro-
gen containing heteroaryl mesogenic compounds [12–14]. Chia et al. reported two liquid
crystalline series based on 6-methoxy quinolines derivatives [15]. Bhoya et al. reported non-
mesogenic behaviour of 8-(4ꢀ-n-alkoxy benzoyloxy) quinolines series which consisted twelve
homologous [16]. Binnemans and his group reported ionic liquid crystals based on quinolin-
ium and isoquinoline derivatives [17]. The numbers of homologous series contain two central
–
= –
–
–
groups; azomethine ( CH N ) and ester ( COO ) linkage groups [18–21].
Continuing our work on the liquid crystal possibilities of the quinoline system, we have
synthesized and studied the LCs properties of newly series contain imine ( CH N ) and
ester ( COO ) as a central linkage group and presence of quinoline core which is isoelectronic
and isogeometric with respect to naphthalene core systems.
–
= –
–
–
2. Experimental
2.1. Materials
For present synthesized homologous series required materials: 4-hydroxy benzaldehyde, 4-
amino benzoic acid purchased from (S.R.L, Mumbai), 8-hydroxy quinoline purchased from
(Sigma Aldrich). Anhydrous K2CO3 was purchased from (Finar Chemical, Ahmedabad), N,
N-dimethyl amino pyridine (DMAP) and Dicyclohexylcarbodiimide (DCC) were purchased
from (Fluka Chemie, Switzerland). Alkyl bromides (R-Br) were purchased from S.R.L. Chem-
icals (Mumbai). All solvents were dried and purified by standard method prior to use.
2.2. Measurements
Melting points were taken on Opti-Melt (Automated melting point system). The FT-IR 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 analyser. The texture images were studied on
a trinocular optical polarising microscope (POM) equipped with a heating plate and digital
camera. 1H NMR spectra was recorded on a 400 MHz in Bruker Advance 400 in the range
of 0.5 ppm – 16 ppm using CDCl3 as solvent. The phase transition temperatures were mea-
sured using Shimadzu DSC-60 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 study, novel syn-
thesized compound is sandwiched between glass slide and cover slip and heating and cooling
rate is (2°C /min) respectively.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
3
Scheme . Synthetic route of series-.
2.3. Synthesis
4-n-alkoxy benzaldehyde (A) was prepared by reported method [22]. 4-((4-alkoxy benzyli-
dene) amino) benzoic acid (B) was prepared by usual established method [23]. Esters (C1 to
C8, C10, C12, C14, C16, C18) were synthesized by a reported method in literature [24]. Thus, the
synthesized target compounds were filtered, washed, dried and purified till constant transi-
tion temperatures is obtain by using an optical polarizing microscope (POM) equipped with
a heating stage. The synthetic route to a series is mentioned in Scheme 1.
... Synthesis of -n-alkoxy benzaldehyde (A)
4-n-alkoxy benzaldehyde (A) was 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 K2CO3 (1.2 equiv.) in dry acetone as a solvent [22].
... -((-alkoxy benzylidene) amino) benzoic acid (B)
4-((4-alkoxy benzylidene) amino) benzoic acid was prepared by refluxing the mixture of (A)
and 4-amino benzoic acid at 3 to 4 hours in presence of ethanol and few drops of acetic acid
[23]. The resultant mixture was filtered, dried, and purified by column chromatography which
was confirmed by IR and 1H NMR analysis.

4
V. S. SHARMA ET AL.
... Synthesis of quinoline--yl--((-n-alkoxy benzylidene) amino) benzoate (C)
Quinoline-8-yl-4-((4-n-alkoxy benzylidene) amino) benzoate (C) was prepared by esterifica-
tion of (B) and 8-hydroxy quinoline by usual established method reported in literature [33].
The appropriate (B) (2.02 mmol) and 8-hydroxy quinoline (C) (0.246 g, 2.02 mmol), dicy-
clohexylcarbodiimide (DCC) (0.457 g, 2.22 mmol) and dimethylaminopyridine (DMAP) in
catalytic amount (0.002 g, 0.2 mmol) in dry CH2Cl2 (DCM) (40 ml) was stirred at room tem-
perature for 48 h. The resultant crude product was purified by column chromatography on
silica gel eluting with dichloromethane: methanol and recrystallization from chloroform until
the constant transition temperatures were observed.
2.3.4. Reaction Scheme
... Analytical data
−1
– – –
–
–
Compound (2a1): FT-IR (KBr) in cm : 3032 ( C H Str in aromatic), 2825(C H Str. in
–
– –
=
OCH3), 1365 and 1236 ( C O Str), 806 disubstituted aromatic ring (-para), 1630 ( CH N,
1
– –
–
–
Str. azomethine group), 1667 ( C O Str.), 2550 ( OH of COOH group). H NMR: δH
–
–
–
(CDCl3, 400 MHz): 3.80 (s, 3 H, CH3 of OCH3 group), 10.32 (s, 1 H, OH group of
–
–
= –
COOH), 8.23 (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 C15H13NO3: Calculate: C; 70.58%, H; 5.09%, O;
18.82%, N; 5.49%, Found: C; 69.62%, H; 4−.916%, O; 18.74%, N; 5.42%.
– – –
Compound (2a10): FT-IR (KBr) in cm : 3031 ( C H Str in aromatic), 681 Polymethy-
–
–
–
– –
lene ( CH2 )n of OC10H21, 1355 and 1230 ( C O str), 821 disubstituted aromatic ring
–
=
– =
–
–
(-para), 1630 ( CH N, Str. azomethine group), 1661 ( C O Str.), 2556 ( OH of COOH
group). H NMR: δH (CDCl3, 400 MHz): 0.88 (t, 2 H, OC10H21 group), 1.31 (q, 3 H,
1
–
–
–
–
OC10H21 group), 1.26–1.29 (m, 12 H, OC10H21 group), 1.71 (P, 2 H, OC10H21 group),
–
–
–
–
= –
4.06 (t, 2 H, OC10H21 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 C24H31NO3: Calcu: C; 75.59%, H; 8.13%, O; 12.59%, N; 3.67%, Found: C; 75.32%,
H; 8.02%, O; 12.52%, N; 3.62%.
−1
– – –
Compound (2a12): FT-IR (KBr) in cm : 3032 ( C H Str in aromatic), 1365 and 1236
– –
–
–
–
( C O str), 644 Polymethylene ( CH2 )n of OC12H25, 808 disubstituted aromatic ring
–
=
– =
–
–
(-para), 1631 ( CH N, Str. azomethine group), 1672 ( C O Str.), 2558 ( OH of COOH
group); H NMR: 0.88 (t, 2 H, OC12H25 group), 1.31 (q, 3 H, OC12H25 group), 1.26–1.29
(m, 14 H, OC12H25 group), 1.71 (P, 2 H, OC12H25 group), 4.06 (t, 2 H, OC12H25 group),
10.68 (s, 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 C26H35NO3: Calcu:
C; 76.28%, H; 8.55%, O; 11.73%, N; 3.42%, Found: C; 76.23%, H; 8.48%, O; 11.68%, N;
1
–
–
–
–
–
–
–
–
= –
3.37%.
−1
– – –
Compound (C3): FT-IR (KBr) in cm : 3032 ( C H Str in aromatic), 1363 and 1231
– –
–
–
–
( C O str), 760 Polymethylene ( CH2 )n of OC3H7, 808 disubstituted aromatic ring
1
–
=
–
–
(-para), 1617 ( CH N, Str. azomethine group), 1730 ( COO group); H NMR: δH
(CDCl3, 400 MHz): 0.88 (t, 3 H, CH3 of OC3H7 group), 1.72 (t, 2 H, OC3H7 group), 4.06
(t, 2 H, OCH2 of OC3H7), 8.32 (s, 1 H, CH N group), 7.06–7.81 (4 H, first phenyl ring),
7.32–8.16 (4 H, second phenyl ring), 8.98 (s, 1 H, Qu-H), 8.05 (s, 1 H, Qu-H), 7.64 (d, 1 H,
Qu-H), 7.60 (d, 1 H, Qu-H), 7.03 (d, 1 H, Qu-H); Elemental analysis of C26H22N2O3: Calcu:
–
–
–
–
–
–
–
=
C; 76.09%, H; 5.36%, O; 11.70%, N; 6.82%, Found: C; 75.98%, H; 5.32%, O; 11.64%, N; 6.76%.
−1
– – –
Compound (C5): FT-IR (KBr) in cm : 3031 ( C H Str in aromatic), 1365 and 1230
– –
–
–
–
( C O str), 644 Polymethylene ( CH2 )n of OC5H11, 808 disubstituted aromatic ring

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
5
1
–
=
–
–
(-para), 1620 ( CH N, Str. azomethine group), 1760 ( COO group); H NMR: δH
–
–
–
(CDCl3, 400 MHz): 0.88 (t, 3 H, CH3 of OC5H11 group), 1.26–1.29 (m, 6 H, OC5H11
–
–
–
–
–
–
group), 1.73 (t, 2 H, CH2 of OC5H11 group), 4.06 (t, 2 H, OCH2 of OC5H11), 8.31
–
=
(s, 1 H, CH N group), 7.06–7.83 (4 H, first phenyl ring), 7.32–8.14 (4 H, second phenyl
ring), 8.98 (s, 1 H, Qu-H), 8.05 (s, 1 H, Qu-H), 7.64 (d, 1 H, Qu-H), 7.60 (d, 1 H, Qu-H), 7.03
(d, 1 H, Qu-H); Elemental analysis of C28H26N2O3: Calcu: C; 76.71%, H; 5.93%, O; 10.95%,
N; 6.39%, Found: C; 76.67%, H; 5.87%, O;−110.89%, N; 6.34%.
– – –
Compound (C10): FT-IR (KBr) in cm : 3031 ( C H Str in aromatic), 1364 and 1236
– –
–
–
–
( C O str), 644 Polymethylene ( CH2 )n of OC10H21, 808 disubstituted aromatic ring
(-para), 1631 ( CH N, Str. azomethine group), 1760 ( COO group); H NMR: δH (CDCl3,
400 MHz): 0.88 (t, 3 H, CH3 of OC10H21 group), 1.26–1.29 (m, 12 H, OC10H21 group),
1.73 (P, 2 H, CH2 of OC10H21 group), 4.06 (t, 2 H, OCH2 of OC10H21), 8.34 (s, 1 H,
1
–
=
–
–
–
–
–
–
–
–
–
–
–
=
CH N group), 7.06–7.83 (4 H, first phenyl ring), 7.32–8.16 (4 H, second phenyl ring), 8.98
(s, 1 H, Qu-H), 8.05 (s, 1 H, Qu-H), 7.64 (d, 1 H, Qu-H), 7.60 (d, 1 H, Qu-H), 7.03 (d, 1 H,
Qu-H); Elemental analysis of C33H36N2O3: Calcu: C; 77.95%, H; 7.08%, O; 9.44%, N; 5.51%,
Found: C; 77.88%, H; 7.01%, O; 9.39%, N;−51.49%.
– – –
Compound (C14): FT-IR (KBr) in cm : 3031 ( C H Str in aromatic), 1364 and 1236
– –
–
–
–
( C O str), 642 Polymethylene ( CH2 )n of OC14H29, 808 disubstituted aromatic ring
(-para), 1631 ( CH N, Str. azomethine group), 1760 ( COO group); H NMR: δH (CDCl3,
400 MHz): 0.88 (t, 3 H, CH3 of OC14H29 group), 1.26–1.29 (m, 14 H, OC14H29 group),
1.73 (P, 2 H, CH2 of OC14H29 group), 4.06 (t, 2 H, OCH2 of OC14H29), 8.34 (s, 1 H,
1
–
=
–
–
–
–
–
–
–
–
–
–
–
–
=
CH N group), 7.06–7.83 (4 H, first phenyl ring), 7.32–8.14 (4 H, second phenyl ring), 8.98
(s, 1 H, Qu-H), 8.05 (s, 1 H, Qu-H), 7.64 (d, 1 H, Qu-H), 7.60 (d, 1 H, Qu-H), 7.03 (d, 1 H,
Qu-H); Elemental analysis of C37H44N2O3: Calcu: C; 78.72%, H; 7.80%, O; 8.51%, N; 4.96%,
Found: C; 78.68%, H; 7.74%, O; 8.47%, N;−41.93%.
– – –
Compound (C16): FT-IR (KBr) in cm : 3031 ( C H Str in aromatic), 1363 and 1240
–
–
–
(-C-O str), 566 Polymethylene ( CH2 )n of OC16H33, 808 disubstituted aromatic ring (-
para), 1631 ( CH N, Str. azomethine group), 1760 ( COO group); H NMR: δH (CDCl3,
400 MHz): 0.88 (t, 3 H, CH3 of OC16H33 group), 1.26–1.29 (m, 18 H, -OC16H33 group),
1.73 (P, 2 H, CH2 of OC16H33 group), 4.06 (t, 2 H, -OCH2- of OC16H33), 8.34 (s, 1 H,
1
–
=
–
–
–
–
–
–
–
–
–
=
CH N group), 7.06–7.82 (4 H, first phenyl ring), 7.31–8.14 (4 H, second phenyl ring), 8.98
(s, 1 H, Qu-H), 8.05 (s, 1 H, Qu-H), 7.64 (d, 1 H, Qu-H), 7.60 (d, 1 H, Qu-H), 7.03 (d, 1 H,
Qu-H); Elemental analysis of C39H48N2O3: Calcu: C; 79.05%, H; 8.10%, O; 8.10%, N; 4.72%,
Found: C; 78.98%, H; 8.04%, O; 8.04%, N; 4.68%.
3. Result and investigation
3.1. POM investigation
The targeted compounds were synthesized by the reaction of 4-((4-n-alkoxy benzylidene)
amino) benzoic acid with 8-hydroxy quinoline. In order to investigate the influence of central
linkage group in presence of quinoline core on the mesophase behaviour of liquid crystalline
compounds. In the present article, we have synthesized and study the effect of linking group
as well as the effect of increasing alkyl chain with rigid core such as benzene and quinoline
core. In present investigation, we have prepared total thirteen homologous (C1 to C8, C12,
C14, C16, C18). The mesophase commences from early C3 homologue. Compounds C3 to C7
display SmC and SmA mesophase, while compound C8, C10, C12, C14, C16, C18 display SmC
as well as nematic mesophase enantiotropically manner. Odd-even effect has been observed

6
V. S. SHARMA ET AL.
Table . Transition Temperature in °C by POM.
Transition temperatures in °C
SmA Nm
Sr.no
R = n-alkyl group
Cr
SmC
Iso













C
C
C
C
C
C
C
C
C
C
C
C
C
·
·
·
·
·
·
·
·
·
·
·
·
·
—
—
—
—
—
—
—
—
·
—
—
—
—
—
—
—
.
.
.
.
.
.
—
—
—
—
—
—
—
·
.
.
.
.
.
.
.
.
.
.
.
·
·
·
·
·
·
·
·
·
·
·
·
·
.
.
.
.
.
.
.
.
.
.
.
·
.
.
.
.
.
—
—
—
—
—
·
·
·
·
·
·
·
·
·
—
—
—
—
—
—
·
·
·
·
·
·
·
·
.
.
·
—
·
(Cr = Solid Crystal, SmC = Smectic C phase, SmA = Smectic A phase, Nm = Nematic phase, Iso = Isotropic phase)
in Cr/M-I transition curve at C5 to C6 homologue in present newly synthesized series. The
transition temperatures of the series are mention in below Table 1.
As a preliminary investigation, the mesophases exhibited by present series were examined
by using a polarising optical microscope. The samples were sandwich between a glass slide
and a cover slip. C1 to C2 homologues in present series does not possess mesophase due to the
high crystallinity and short alkyl spacer at left side chain. The nonmesomorphicity of C1, C2
homologue is attributed to the presence of low magnitudes of intermolecular dispersion forces
and low magnitudes of dipole-dipole interactions leading to high crystallising tendency which
causes abrupt to breaking the crystal lattices due to unsuitable and unfavorable magnitudes
of anisotropic forces of intermolecular attractions. Thus, irregular breaking of crystal lattices
and suddenly takes place at relatively higher temperature. Thus, crystalline solid state directly
converted into isotropic phase without displaying any LC phase.
The phase diagram were plotted against transition temperature versus the number of car-
bon atoms present in n-alkyl chain in left terminal end group (-OR) is mention in below
Figure 1. The phase diagram shows Cr-M/I, SmC-SmA, SmA-N transition curve drawn by
the linking the transition temperatures points. Cr-M/I transition curve initially decreasing
as number of alkyl chain in present series is increase. Nematic mesophase commences from
C8 homologue. Nm-I transition curve shows descending tendency as increasing alkyl chain
length. The SmC-SmA transition curve starts descends at C4 homologue and then ascends to
C5 homologue this is due to the presence of odd-even parity of methylene group in n-alkyl
chain length of alkoxy group. Odd-even effect is present in SmC-SmA and N-I transition
curve. N-I transition curve starting with descending tendency at C5 homologue and then
continued to descending tendency upto last C18 homologue. It can be seen that in this homol-
ogous series the transition temperature of present synthesised series is decrease from lower
Table . Nematic phase of compound C, C, C, C and C by miscibility method.
Sr. No.
Homologue
Texture

C
Rod type
Threaded
Rod type
Mosaic type
Threaded
Mosaic type





C
C
C
C
C

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
7
Figure . Phase diagram of series-.
homologue to higher homologue, this is because of increasing the number of methylene unit
–
–
CH2 in right terminal group which increasing its chain length and causes more flexibil-
ity and polarizability. The molecular rigidity due to presence of two benzene core and third
quinoline ring and presence of two central bridges are constant throughout the novel series for
homologues, but the changing molecular length from homologue to homologue in the same
series due to changing number of methylene units in n-alkyl ‘R’ chain of –OR group induces
flexibility. Thus changing trends in mesomorphic behaviours of a present series from homo-
logue to homologue is attributed to the effective flexibility of each azomethine-ester linking
groups based molecules in present series.
... Nematic mesophase by miscibility method
The nematic mesophase in comp. C8 to C18 were also confirmed by using miscibility method
which was mention in below Table 2. Comp.C10 shows threaded type nematic phase whereas
in comp.C12, rod type textural image was seen. Comp. C14 homologue shows rod type textural
pattern of nematic phase. Comp.C16 to C18 shows threaded type textural pattern of nematic
mesophase.
... Textural study
The solid samples held between an untreated glass slide and a coverslip were heated to their
isotropic phase and cooled slowly. As shown in Figure 2, a threaded type line textural image of
nematic phase of compound C10 seen at 71.0°C on cooling condition. Compound C18 displays
rod type textural pattern of SmA phase at 116.0°C on cooling condition. Compound C6 shows
rod type textural pattern of SmA phase at 114.0°C on cooling condition while in compound
C14, a mosaic type textural image of nematic phase observed at 72.0°C on cooling condition. It
can be noted that higher member of series displayed nematic mesophase as compare to lower
membered of the series. The nematic mesophase is attributed to the suitable magnitudes of
end to end intermolecular anisotropic forces of attractions and closeness as a consequence of
favorable molecular rigidity, linearity due to the presence linking group and flexibility cause

8
V. S. SHARMA ET AL.
Figure . Microphotographs of the optical textural pattern (a) threaded line type texture image of com-
pound C, (b) SmA phase of compound C; (c) SmA phase of compound C and (d) mosaic type textural
pattern of comp.C.
by the presence of left side chain generate permanent dipole moment across the long molec-
ular 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 [25].
... Comparative study and thermal stability
–
= –
In order to examine the effect of schiff base ( CH N ) linkage group, the LC behaviour
of present synthesized series-1 was compared with structurally similar reported series-2 as
shown in Figure 3. Homologous series-1 and X are identical with respect to three phenyl
Figure . Structurally comparison with previously reported series.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
9
Figure . Ball-stick model of series- and series-.
rings, two central bridges joining phenyl rings and two flexible terminal end groups (-OR
–
and OC16H33). But, they differ with respect to their geometrical shapes linear and nonlinear
respectively for the same homologues from series to series. Therefore they differ with respect
to combined effects of molecular rigidity and flexibility, including intermolecular distance
and molecular polarizability which operates LC behaviours of series. Homologous series-2
are identical with series-1 at second ester linkage group and quinoline ring at terminal side.
Series-2 display nonliquid crystalline behaviour. The molecular length of series-2 is lower as
–
= –
compare to series-1.Introducing of azomethine ( CH N ) linkage group in series-1 which
increase the length of molecules as compare to series-2 causes mesomorphism with good ther-
mal stability. Thus, mesomorphic (LC) properties are attributed to the magnitudes of differing
features like geometrical shapes, molecular rigidity and flexibility of molecules. Figure 4 rep-
resents the ball-stick model which indicates the geometrical shape and molecular length of
series-1,-2.
Table 3 shows the average thermal stabilities and mesophase range of newly homologous
Series (C1 to C8, C10, C12, C14, C16, C18). The N–I thermal stability of Series is 107.66°C. The
SmC–SmA thermal stability is 115.2°C. Thermal stability of SmC–N phase is 85.0°C. How-
ever, the SmA-I thermal stability of Series is 144.0°C. The average mesophase length of present
series is 44.0°C and 34.0° C respectively. The thermal stability of SmA-I and SmC-SmA phase
is higher than the thermal stability of N-I and SmC-N phase. The ester linking group favors the
lamellar packing due to the dipole–dipole interaction which ultimately generated the smectic
phase [26].
Table . Average thermal stability in °C.
Series
Series-
Series-
SmC-SmA
SmC-N
.
.
—
—
Commencement of SmC phase
SmA-I
Commencement of SmA phase
N-I
Commencement of Nematic phase
Degree of
mesomorphism in °C from minimum to maximum
C
.
C
.
C
. to .
C C
—
—
—

10
V. S. SHARMA ET AL.
Figure . DSC thermogram of (a) C, (b) C, (c) C and (d) C homologue.
3.2. DSC analysis
DSC is a valuable method for detecting phase transitions. The thermal behaviour of novel
homologues series were confirmed by DSC analysis shown in below Figure 5. Thermogram is
traces in both heating and cooling condition. Microscopic transition temperature values are
similar to the DSC data.
On heating condition, C5 homologue shows two endothermic peaks on heating and cool-
ing condition. The traced two endothermic peaks correspondence to the SmC and SmA
phase. First endothermic peak observed at 101.12°C, which indicates the presence of SmC
phase. While second endothermic peak observed at 113.51°C to confirmed the changing of
SmC phase into SmA phase.On cooling condition, again two endothermic peaks traced at
96.51°C and 114.82°C, which was further confirmed by using POM study. Com.C8 shows
two significant peaks on heating and cooling condition. First endothermic peak is observed at
74.08°C and second endothermic peak trace at 92.73°C on heating condition. While on cool-
ing condition, two endothermic peaks observed at 69.93°C and 95.84°C. Comp.C12 shows two
endothermic peaks at 66.91°C and 86.98°C on heating condition while, on cooling condition
two endothermic peaks traced at 64.22°C and 88.23°C. For comp. C18, two endothermic peaks
trace on heating and cooling condition. On heating condition first two endothermic peaks
trace at 53.28°C and 72.37°C while on cooling condition, it traced at 52.85°C and 71.34°C
to indicates the presence of SmC and nematic mesophase which was confirmed by POM
analysis.
Transition temperature obtained by DSC analysis at heating and cooling condition and the
value of enthalpy and entropy is mention in Table 4. Molecules of every homologue randomly
oriented in all possible directions with high order of disorder or entropy (ꢀS = ꢀH/T) beyond
isotropic temperature and the enthalpy value (ꢀH). But, at cooled condition, the same from

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
11
Table . Transition temperature (°C) and enthalpy (J g−) and entropy change (J g−k−) by DSC
measurement.
Homologuesor
Comp.
Heating
scan(°C)
Cooling
scan(°C)
ꢀS(J
ꢀS(J
Transition
ꢀH (−Jg−
)
ꢀH (Jg−
)
g
−k−
)
g
−k−
)
C5
Cr-SmC
SmC-SmA
SmA-I
Cr-SmC
SmC-N
N-I
Cr-SmC
SmC-N
N-I
.
.
>.
.
.
>.
.
.
> .
.
.
>.
.
.
—
.
.
—
.
.
—
.
.
—
.
.
.
.
.
.
.
.
.
.
.
.
.
.
—
.
.
—
.
.
—
.
.
—
.
.
.
.
.
.
.
.
.
.
.
.
.
.
—
.
.
—
.
.
—
.
.
—
C8
C12
C18
Cr-SmC
SmC-N
N-I
and below isotropic temperature, the mesophase is persisted to appear reversibly at high or
lower temperature at observed during heating and cooling condition. The enthalpy values
also indicate the crystal to mesophase and mesophase to isotropic transition in compounds
C5, C8, C12 and C18. The mesophase observed enantiotropically manner in present series.
4. Conclusion
In this article, we have presented the synthesis and characterization as well as the mesomor-
phic behaviour quinoline based homologues series viz. quinoline-8-yl-4-((4-n-alkoxy ben-
zylidene) amino) benzoate (n = 1 to 8, 10, 12, 14, 16, 18), which comprised of Schiff base
ester moieties as linking group and alkoxy side chain group. The synthesized compounds
with having short alkyl spacer exhibits SmC and SmA phases, while in long alkyl spacer com-
pounds exhibits SmC and N mesophases. An additional feature found in the present series is
–
= –
–
–
that the presence of azomethine ( CH N ) and ester ( COO ) group as a central part and
terminally quinoline core leads more thermal stable mesophase.
Acknowledgement
Authors acknowledge thanks to Dr. R.R.Shah, principal and management of K. K. Shah Jarodwala Man-
inagar Science College, Ahmedabad. Authors are also thankful to NFDD Centre for providing analytical
and spectral services.
References
[1] Macros, M., Omenat, A., Serrano, J. L., & Ezcurra, A. (1992). Adv.Mater., 4, 285.
[2] Hird, M., Toyne, K. J., & Gray, G. W. (1993). Liq.Cryst., 14, 741.
[3] Hird, M., Toyne, K. J., Gray, G. W., Day, S. E., McDonnell, D. G. (1993). Liquid Crystal., 15, 123.
[4] Lauk, U., Scrabol, P., & Zollinger, H. (1983). Helv.Chim.Acta., 66, 1574.
[5] Sierra, J., Serrano, J. L., Ros, M. B., Ezcurra, A., & Zubia, J. (1992). J.Am.Chem.Soc., 114, 7645.
[6] Zuniga, C., Belmar, J., Parra, M., Remirez, A., Decap, J., Ros, B., & Serrano, J. L. (1996). Liquid
Crystals., 20, 253.
[7] Leardini, R., Nanni, D., Pedulli, G. F., Tundo, A., & Zanardi, G. (1987). Liq.Cryst., 2, 625.
[8] Zuniga, C., Bartulin, J., Muller, H. J., Schumacher, E., & Taylor, T. R. (1991). Mol.Cryst.Liq.Cryst.,
206, 131.

12
V. S. SHARMA ET AL.
[9] Zuniga, C., Belmar, J., Parra, M., Ramirez, A., Decar, J., Ros, B., & Serano, J. L. (1996). Liq.Cryst.,
20, 253.
[10] Lin, H. C., Lai, L. L., Hsieh, W. P., & Huang, W. Y. (1997). Liquid Crystal., 22, 661.
[11] Zanardi, G. (1987). Liquid Crystal., 2, 625.
[12] Chia, W. L., & Cheng, Y. W. (2008). Heterocycles., 75, 375.
[13] Chia, W. L., Chia, W. L., & Chang, C. H. (2009). Mol.Cryst.Liq.Cryst., 506, 47.
[14] Chia, W. L., Liao, K. H., & Ho, C. I. (2009). Liq.Cryst., 36, 557.
[15] Chia, W. L., Ye, F. J., & Chen, E. C. (2013). Liquid Crystals., 40, 989.
[16] Bhoya, U. C., Vyas, N. N., & Doshi, A. V. (2012). Mol.Cryst.Liq.Cryst., 552, 104.
[17] Lava, K., Evrard, Y., Hecke, K. V., Meervelt, L. V., & Binnemans, K. (2012). RSC Advance., 2, 8061.
[18] Ha, S. T., Ong, L. K., Wong, J. P. W., Yeap, G. Y., Lin, H. C., Ong, S. T., & Koh, T. M. (2009). Phase
Transition., 82, 387.
[19] Yeap, G. W., Ha, S. T., Lin, P. L., Ito, M. M., & Sanehisa, S. (2004). Mol.Cryst.Liq.Cryst., 423, 73.
[20] Dave, J. S., Kurian, G. (1997). Mol.Cryst.Liq.Cryst., 175, 42.
[21] Yelamaggad, C. V., Mathews, M., Negamani, A., Rao, S., Prasad, S. K., Findeisen, S., & Weissflog,
W. (2007). J.Mater.Chem., 17, 284.
[22] Sharma, V. S., & Patel, R. B. (2016). Mol.Cryst.Liq.Cryst., 630, 58.
[23] Furniss, B. S., Hannford, A. J., Smith, P. W. G., & Tatchell, A. R. (Revisors). (1989). Vogel’s Text-
book 245 of Practical Organic Chemistry (4th ed.), 563, Longmann Singapore Publishers Pvt. Ltd.,
Singapore.
[24] Uhood, J. A. (2011). International Journal of Molecular Science., 12, 3182.
[25] Suthar, D. M., & Doshi. A. V. (2013). Mol. Cryst. Liq. Cryst., 571, 1.
[26] Gray, G. W. (1962). Molecular Structure and Properties of Liquid Crystals, Academic Press, London.