Synthesis and characterization of novel rod-like ester-based liquid crystalline homologous series: Effect of tert-butyl tail on mesomorphism

Article abstract of DOI:10.1080/15421406.2020.1856507

A new rod-like homologous series consisting twelve compounds with central ester linkage and terminal tert-butyl group, tert-butyl [4-(4’-n-alkoxybenzoyloxy)benzoates] has been synthesized and characterized through standard spectroscopic techniques like UV, FT-IR, ¹HNMR, DSC, POM, and XRD. Methoxy and ethoxy derivatives are nonmesogenic. Nematic mesophase commences as enantiotropy from propyloxy derivative and persists up to the octadecyloxy derivatives. Smectic A mesophase commences as monotropy from propyloxy to the octadecyloxy derivatives. The mesomorphic properties of present series are compared with other structurally related series to evaluate the effect of terminal tert-butyl group on mesomorphism. Two derivatives are subjected to in?vitro antimicrobial activity.

Full text of DOI:10.1080/15421406.2020.1856507

Molecular Crystals and Liquid Crystals
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/gmcl20
Synthesis and characterization of novel rod-like
ester-based liquid crystalline homologous series:
Effect of tert-butyl tail on mesomorphism
Shavi Thakur & Hemant N. Patel
To cite this article: Shavi Thakur & Hemant N. Patel (2020) Synthesis and characterization
of novel rod-like ester-based liquid crystalline homologous series: Effect of tert-butyl
tail on mesomorphism, Molecular Crystals and Liquid Crystals, 712:1, 76-89, DOI:
10.1080/15421406.2020.1856507
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MOLECULAR CRYSTALS AND LIQUID CRYSTALS
2020, VOL. 712, NO. 1, 76–89
https://doi.org/10.1080/15421406.2020.1856507
Synthesis and characterization of novel rod-like ester-based
liquid crystalline homologous series: Effect of tert-butyl tail
on mesomorphism
Shavi Thakura and Hemant N. Patelb
b
aShri Maneklal M. Patel Institute of Science and Research, Gandhinagar, Gujarat, India; Kadi Sarva
Vishwavidhyalaya (Kadi) University, Gandhinagar, Gujarat, India
KEYWORDS
ABSTRACT
Enantiotropic; in vitro
activity; liquid crystal;
nematic; smectic A; tert-
butyl group
A new rod-like homologous series consisting twelve compounds
with central ester linkage and terminal tert-butyl group, tert-butyl [4-
(4’-n-alkoxybenzoyloxy)benzoates] has been synthesized and charac-
terized through standard spectroscopic techniques like UV, FT-IR,
1HNMR, DSC, POM, and XRD. Methoxy and ethoxy derivatives are
nonmesogenic. Nematic mesophase commences as enantiotropy
from propyloxy derivative and persists up to the octadecyloxy deriv-
atives. Smectic A mesophase commences as monotropy from propy-
loxy to the octadecyloxy derivatives. The mesomorphic properties of
present series are compared with other structurally related series to
evaluate the effect of terminal tert-butyl group on mesomorphism.
Two derivatives are subjected to in vitro antimicrobial activity.
1. Introduction
A liquid crystalline state [1] is a state which is an intermediate state between liquid and
solid and is of great importance to universal bodies in different areas of relating science
and other technological applications [2, 3].Some substances exhibit an intermediate state
of matter with molecular ordering in between that of conventional crystalline solid and
isotropic liquid phases, and this state of matter is called a liquid crystal state or meso-
morphic state [4, 5]. Because of the peculiar physical properties and different ranges of
temperature, the nematic phase behavior in liquid crystal plays an important role in
generation of new liquid crystal displays (LCDs). A small change in the molecular
arrangements is affected by the mesomorphic behavior of organic compounds. The the-
oretical study of many series was very informative to have an idea about chemical con-
stitution in nemactogenic and smectogenic compounds [6, 7]. The orientation of
molecule in nematic phase is toward a particular direction. The molecular orientation
can be achieved in portable approach after applying an electric or magnetic field [8].
Calix [4] arene core was prepared by condensing Schiff base derivatives of 4-n-alkoxy-
benzaldehyde and 4-aminobenzoic acid at lower rim of tert-butyl calix [4] arene and
studied the mesomorphic properties of calix [4] arene Schiff base ester derivatives along
CONTACT Hemant N. Patel
hemant_2patel@yahoo.co.in
Kadi Sarva Vishwavidhyalaya (Kadi) University,
Gandhinagar, Gujarat, India.
ß 2021 Taylor & Francis Group, LLC

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
77
with the biological investigations [9]. Calixarene with tunable 3D shaped cavities which
helps in creating supramolecular platform after crown ether and cyclodextrin [10]. A
review on lower rim substituted calixarenes along with their applications was reported
by Menon et al. [11]. Recently, antimicrobial activity of p-tetra nitro calix [4] arene
derivatives was reported by Menon et al. [12]. Doshi et al. synthesized homologous ser-
ies containing ester and vinyl ester linkage group [13, 14]. Vinay et al. reported the
effect of tail or lateral group on mesomorphism for various homologous series contain-
ing alkoxy benzoates and alkoxy cinnamates [15–19]. Earlier mesogenic esters with
straight and branched alkyl chains have been reported [20–22]. Calix [4] arene-based
chemsensors with high sensitivity and power were reported to sense analytes [23]. Calix
[4] arene system with fluorescence mechanism is mainly PET [24], FRET [25], PCT
ꢀ
[26], and ICT [27] for molecular recognition. E. Sinkovec et al. reported a liquid–liquid
phase transfer catalyzed (PTC) esterification reaction of 4-t-butylphenol in aqueous
phase and 4-methoxybenzoyl chloride in organic phase with product 4-t-butylphenyl 4-
methoxy benzoate in a micro channel under parallel laminar flow conditions by using
tetra butyl ammonium bromide as PTC developing a 3D mathematical model consider-
ing convection in the flow directions and diffusion in spatial directions [28].
From earlier researches, Wang et al. [29], Asai et al. [30], Wang et al. [31],
Bhattacharya et al. [32], and Yang et al. [33] reported about interfacial mass transfer
and mathematical modeling. For estimating diffusion coefficients, Wilke–Chang’s empir-
ical correlation was used as follows:
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
WBMWBT
DAB ¼ 7:4 ꢀ 10ꢁ8
ȠBV0:6
A
where A and B denote solute and solvent (Li and Carr [34]).
Ju Hyun Kim et al. reported a CO-gas-free alkoxy carbonylation of aryl iodides in pres-
ence of [Rh(COD)Cl]2DPEPhos catalytic system and an alcohol with/without an aldehyde
[35]. Presence of both alcohol and aldehyde leads to high yield of alkoxycarbonylated prod-
ucts while without these two, leads to have moderate yield. Also, phenol leads to phenoxy-
carbonylation products with high yields. Esters from aryl iodides and various alcohols in
phenoxycarbonylation reaction in which aldehyde acted as a sole source of CO yield a prod-
uct 4-t-butylphenyl 4-methoxy benzoate (30%) as one of the substrate leads to a conclusion
that phenyl hydroxyl groups is more reactive than benzyl hydroxyl group and electron-defi-
cient phenols are more reactive than electron-rich phenols [36]. A plausible reaction can be
drawn for alkoxycarbonylation of an aryl halide with rhodium compound, an alcohol and
an aldehyde [37–39]. Recently, some studies have been reported [28, 35], and the research
group reported various aspects related to their research field but no mesomorphic properties
were mentioned for LC. In our present studies, we have synthesized newly ester-based hom-
ologous series with varying left alkoxy (-OR) side chain while keeping the group fixed at ter-
minal tert-butyl tail showing great mesogenic properties related to LC studies.
2. Experimental
2.1. Materials
For present synthesized homologous series, 4-hydroxy benzoic acid was purchased from
S.R.L., Mumbai and para tert-butyl phenol from Sigma–Aldrich. N-bromo alkanes

78
S. THAKUR AND H. N. PATEL
(S.R.L., Mumbai), methanol, pure thionyl chloride (SOCl2), potassium hydroxide (Finar
Chemicals, India), and pyridine, required for synthesis, were used as received along
with previously dried and purified solvents.
2.2. Measurements
Microanalysis of the compounds was performed on a Coleman Carbon/Hydrogen ana-
lyzer. The FT-IR spectral data were obtained for KBr pellets, using Shimadu IR-408
spectrophotometer.1H NMR spectral data were recorded on a Perkin–Elmer R-32 spec-
trometer using tetramethylsilane (TMS) as internal reference standard. The chemical
shifts are shown in d (ppm) downfield from the reference, and CDCl3 was used as solv-
ent. The beautiful images were captured on a trinocular optical polarizing microscope
(POM) (Leitz Laborlux 12 POL) fitted with heating plate and a digital camera. The tran-
sition enthalpies were recorded by cryo-DSC model DSC 822e, Mettler Toledo,
Switzerland, having stare software system at a heating and cooling rate of 5 ꢂC minꢁ1
with pure indium as a standard for calibration. The compound is sand-witched between
the two glass slides and a cover slip at heating, and cooling rate is 2 ꢂC minꢁ1
respectively.
,
The synthetic route to compounds of Series I is illustrated in Scheme 2.
2.3. Synthesis
4-n-alkoxy benzoic acids (A) were prepared from 4-n-hydroxy benzoic acids by applying
a Williamson’s ether synthesis protocol [40] by refluxing the mixture of 4-n-hydroxy
benzoic acid (one equiv.) with corresponding n-alkyl bromide (1 equiv.) in presence of
KOH (1.5 equiv.) and methanol as a solvent [40]. 4-n-alkoxy benzoyl chloride (B) was
prepared by heating corresponding acids with excess of thionyl chloride under reflux
for 2 hrs [41]. The tert-butyl phenol (15 mmol) was dissolved in dry pyridine (10 ml),
and a cold solution of an appropriate 4-n-alkoxy benzoyl chloride (15 mmol) (B) was
added slowly while stirring in an ice bath. Before acidification with cold 1:1 aq. HCl,
the mixture kept undisturbed overnight at room temperature. The insoluble was
removed through filtration. The elute was obtained after the removal of excess solvent
using TLC plates (thin layer þ chromatography Merck Kiesel gel 60 F254 pre-coated
plates) for purity check. After extraction, the obtained residue was separated by column
chromatography on silica gel using proportion (95:5) of petroleum ether and ethyl acet-
ate, and then, it was crystallized repeatedly from methanol till constant transition tem-
perature was obtained .All twelve synthesized compounds of present Series I are
1
confirmed by using spectral and analytical techniques like UV, FT-IR, HNMR, and
XRD (n-dodecyloxy derivative of Series I), and were found to be satisfactory with the
proposed structure.
Typical spectral data of various compounds of Series I are as follows:
Series I: tert-butyl [4-(4’-n-hexyloxy) benzoate]
UV Spectrum (MDC) nm: 280.
IR spectrum (KBr) ꢀmax/cmꢁ1: 2932, 1724 (-COO-), 1627, 1258, 846,643.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
79
Scheme 1. The general formula is shown.
Scheme 2. Synthetic route to Series I compounds.
1H NMR: dH(CDCl3,400 MHz): 0.89 (t, 3H, -CH3), 1.32-1.48 (m, 6H, 3ꢀ -CH2), 1.32 (s,
9H, - C(CH3)3), 1.80 (p, 2H, -CH2), 4.03 (t, 2H, -OCH2), 6.93 (d, 2H, ArH), 7.71 (d, 2H,
ArH) , 7.91 (d, 2H, ArH), 8.05 (d, 2H, ArH).

80
S. THAKUR AND H. N. PATEL
Series I: tert-butyl [4-(4’-n-decyloxy)benzoate]
UV Spectrum (MDC) nm: 280.
IR spectrum (KBr) ꢀmax/cmꢁ1: 2918, 1732 (-COO-), 1601, 1515, 1464, 1286, 1249,
1160, 816.
1H NMR: dH(CDCl3,400 MHz): 0.88 (t, 3H,-CH3), 1.24-1.47 (m, 14H, 7ꢀ -CH2), 1.31 (s,
9H, - C(CH3)3), 1.80 (p, 2H, -CH2), 4.03 (t, 2H, -OCH2), 6.93 (d, 2H, ArH), 7.14 (d, 2H,
ArH) , 7.45 (d, 2H, ArH), 8.05 (d, 2H, ArH).
Series I: tert-butyl [4-(4’-n-dodecyloxy)benzoate]
UV Spectrum (MDC) nm: 270.
IR spectrum (KBr) ꢀmax/cmꢁ1: 2926, 1735 (-COO-), 1607, 1511, 1465, 1254, 1168,
1069, 842.
1H NMR: dH(CDCl3,400 MHz): 0.88 (t, 3H,-CH3), 1.27-1.56 (m, 18H, 9ꢀ -CH2),1.31 (s,
9H, -C(CH3)3),1.79 (p, 2H, -CH2), 4.04 (t, 2H, -OCH2), 6.97 (d,2H, ArH), 7.11 (d, 2H,
ArH), 7.61 (d, 2H, ArH), 8.15 (d, 2H, ArH).
Series I: tert-butyl [4-(4’-n- tetradecyloxy)benzoate]
UV Spectrum (MDC) nm: 260.
IR spectrum (KBr) ꢀmax/cmꢁ1: 2918, 1732 (-COO-), 1601, 1515, 1464, 1286, 1249,
1160, 816.
1H NMR: dH(CDCl3,400 MHz): 0.88 (t, 3H,-CH3), 1.26-1.47 (m, 22H, 11ꢀ -CH2),1.31 (s,
9H, -C(CH3)3),1.80 (p, 2H, -CH2), 4.02 (t, 2H, -OCH2), 6.92 (d, 2H, ArH), 7.12 (d, 2H,
ArH), 7.43 (d, 2H, ArH), 8.03 (d, 2H, ArH).
Series I: tert-butyl [4-(4’-n- hexadecyloxy)benzoate]
UV Spectrum (MDC) nm: 260.
IR spectrum (KBr) ꢀmax/cmꢁ1: 2918, 1732 (-COO-), 1601, 1515, 1464, 1286, 1249,
1160, 816.
1H NMR: dH(CDCl3,400 MHz): 0.88 (t, 3H,-CH3) , 1.26-1.45 (m, 26H, 13ꢀ -CH2), 1.31 (s,
9H, -C(CH3)3), 1.80 (p, 2H, -CH2), 4.00 (t, 2H, -OCH2), 6.91 (d, 2H, ArH), 7.09 (d, 2H,
ArH) , 7.42 (d, 2H, ArH), 8.05 (d, 2H, ArH).
Series I: tert-butyl [4-(4’-n-octadecyloxy)benzoate]
UV Spectrum (MDC) nm: 250.
IR spectrum (KBr) ꢀmax/cmꢁ1: 2918, 1736 (-COO-), 1604, 1511, 1470, 1255, 1205,
1167, 844.
1H NMR: dH(CDCl3,400 MHz): 0.80 (t, 3H,-CH3), 1.18-1.41 (m, 30H, 15ꢀ -CH2), 1.31 (s,
9H, -C(CH3)3), 1.76 (p, 2H, -CH2), 3.96 (t, 2H, -OCH2), 6.88 (d, 2H, ArH), 7.04 (d, 2H,
ArH) , 7.34 (d, 2H, ArH), 8.06 (d, 2H, ArH).
3. Results and discussion
3.1. Optical microscopy studies
On the basis of earlier attempts, the optical microscopic studies conclude that the meso-
phases exhibited by the compounds of Series I and Series A. The structurally related

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
81
Figure 1. Structurally similar Series I and Series A.
Series I and comparative Series A are shown in Figure 1. The space filling diagrams of
both Series I and Series A are shown in Figure 2.n-Methoxy and n-ethoxy derivatives
are nonmesogenic and change directly into liquid state, that is enantiotropy (no meso-
phase exists) due to the possibility of high rate of crystallization because of high melt-
ing point.
The non-mesomorphicity of n-methoxy and n-ethoxy derivatives with short alkyl
chain length might be because of the lower intermolecular dispersion forces and lower
dipole–dipole interfaces providing great isotropic crystallizing tendency. Thus, during
heating, irregular and further splitting of crystal lattices directly reach to its isotropic
phases, while during cooling conditions, freezing starts from isotropic conditions with-
out showing any liquid crystalline phases. The present investigation includes the effect
of terminal-side tert-butyl group with linear chalconyl ester group with variable flexibil-
ity on mesomorphism. In addition, compounds showing classical schlieren pattern of
the nematic mesophase commence as enantiotropy from n-propyloxy and persist up to
the n-octadecyloxy derivative of the series. Smectic A mesophase with focal conic pat-
tern commences as monotropy from n-propyloxy and persists up to the n-octadecyloxy
derivative of the series. Using optical polarizing microscope, phases can be seen by mak-
ing thin film samples by sandwiching novel compound between glass slide and cover
slip. Nematic phase can be observed as enantiotropy, and all the compounds from n-
propyloxy to n-octadecyloxy show droplet-type texture. On cooling, isotropic liquids of
Series I compounds show the classical schlieren texture of the nematic phase like in
form of small droplets in Figure 3a.
On further cooling, all the compounds from n -propyloxy to the n-octadecyloxy
exhibit focal conic texture of SmA mesophase in Figure 3b and c. While in Series A,
nematic mesophase starts from n-tetradecyloxy to n-octadecyloxy homologous, in n-tet-
radecyloxy, fan-like rod nematic mesophase in heating and cooling conditions and
droplet-type texture of nematic mesophase in n-hexadecyloxy and rod-like texture of
nematic phase in n-octadecyloxy, respectively. SmA phase with broken fan-like texture
can be seen from methoxy to n-dodecyloxy along with the SmC mesophase in all the
thirteen compounds [42]. The existence of nematic mesophase is due to greater terminal
attractions. As the number (n) increases, alkyl chain length increases and polarizability
increases with the increase in intermolecular van der Waals attractions. But the lateral

82
S. THAKUR AND H. N. PATEL
Figure 2. Space filling diagrams of Series I and Series A.
attractions are more predominant over terminal attractions [43]. Thus, molecules
achieve layered structure in fluid conditions while heating further increases in tempera-
ture, weakens the strict adherence to layered form due to greater thermal vibrations,
thus achieving more fluid nature. At a certain temperature, breaking of layered structure
occurs but still maintains end-to-end parallel orientation which leads to give nematic-
threaded texture to the homologous. But at a certain temperature, SmA mesophase
exists due to the increase in the alkyl chain length at one end and as ratio of terminal
to lateral attractions decreases, there are less chances of achieving nematic mesophase
and at that particular stage there are more chances of achieving SmA mesophase only.
Figure 4 shows the plot of transition temperature and number of carbon atoms. A
sharp decrease in crystal-mesophase/isotropic transition temperature can be seen as the
length of terminal alkyl chain(-OR) increases giving enantiotropic behavior from third
member of Series I. Due to the change in (-R) group from n-methoxy to last member
n-octadecyloxy, there exists a change in the mesomorphic properties while keeping the
central ester group at the same position.
Nematic-isotropic (N–I), (SmA–N) as well as SmA-I transition temperatures decrease
exhibiting the usual odd–even effect. Also, in comparative Series A, the same odd–even
effect can be seen [42] in phase diagram.
Gray et al. described a view on higher nematic phase transition curve with the
increase in anisotropy of the polarizability and increase in intermolecular cohesive
forces due to the increase in the side chain of the molecule. The molecule becomes
strained as oxygen atom will bump into the nonbonded side of the adjacent hydrogen
of ring causing twist around the carbonyl bond. This will make the molecule broad, and
benzene ring of Series I becomes out of plane [43].
The nematic mesophase exists due to the thermal vibrations (DH), also due to the
anisotropic end-to-end intermolecular attractions helping the molecules to move on the
surface in parallel orientation which can be seen on the top of slide [44].
For confirmation of the phase transition and thermal behavior, DSC is most widely
used and a valuable tool. Thermograms obtained in heating and cooling conditions are
in close agreement with the microscopic temperature values in heating and cooling con-
ditions. For Series I, on heating cycle, the compound 8 showed three peaks at 99.46 ꢂC

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
83
Figure 3. Optical textures of the compounds of the present series. Optical textural photographs of (a)
schlieren texture of nematic mesophase (Series I; n ¼ 14) at 99 ꢂC, (b) focal conic texture of SmA mes-
ophase (Series I; n ¼ 14) at 95 ꢂC on cooling, and (c) focal conic texture of SmA mesophase (Series I;
n ¼ 18) at 75 ꢂC on cooling.
Figure 4. Phase diagram of Series I.
(DH ¼ 89.15 J/g), 102.16 ꢂC (DH ¼ 68.40 J/g), and 118.00 ꢂC (DH ¼ 70.22 J/g), which cor-
responds to the Cr–SmA, SmA–N, and N–I transitions, respectively. For Series I, on
heating cycle, the compound 13 showed three peaks at 61.61 ꢂC (DH ¼ 61.49 J/g),
72.50 ꢂC (DH ¼ 58.34 J/g), and 90.00 ꢂC (DH ¼ 61.56 J/g), which corresponds to the

84
S. THAKUR AND H. N. PATEL
Table 1. Transition temperatures (ꢂC) of the Series I compounds.
Compound No.
R ¼CnH2nþ1 n ¼
Cr
SmA
N
I
1
2
3
4
5
6
7
8
1
2
149
151
143
142
130
119
121
118
110
108
108
96
–
–
–
–
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
3
4
5
6
7
8
10
12
14
16
18
(ꢃ
(ꢃ
(ꢃ
(ꢃ
(ꢃ
(ꢃ
(ꢃ
(ꢃ
(ꢃ
(ꢃ
(ꢃ
112)
113)
111)
104)
106 )
102)
99)
89)
95)
88)
72)
137
125
113
112
108
105
104
102
99
9
10
11
12
13
94
83
89
() ¼ monotropic value; Cr ¼ crystalline solid; SmA ¼ smectic A phase; N ¼ nematic phase; I ¼ isotropic liquid phase; ꢃ,
phase exists; -, phase does not exist.
Table 2. Transition temperature (ꢂC), and enthalpy (-Jgꢁ1) and entropy (-Jgꢁ1Kꢁ1) change by DSC
measurement of Series I and of comparative Series A. DSC data for Series I and A compounds.
Series
Compound
8
Transition
Peak temp/ ꢂC
DH/ Jg-1
DS/ Jg-1K-1
I
Cr–SmA
SmA–N
N–I
Cr–SmA
SmA–N
N–I
Cr–SmC
SmC–SmA
SmA–I
Cr–SmC
SmC–N
N–I
99.46
102.16
118
89.15
68.40
70.22
61.49
58.34
61.56
37.92
9.21
0.2393
0.1556
0.1795
0.1837
0.1688
0.1695
0.1003
0.0227
0.0274
0.0899
0.0202
0.0251
18
8
61.61
72.50
90.00
105.02
113.12
>140
85.91
98.23
>110
A
11.34
32.29
7.53
18
9.62
Cr–SmA, SmA–N, and N–I transitions, respectively. On cooling also, the compound 13
showed significant peaks for the I-N, N-SmA, and SmA-Cr transitions, respectively,
which was further confirmed by POM studies.
The results are recorded in Table 2.
On heating, hexyloxy homolog shows endothermic peak at 112 ꢂC indicates presence
of nematic phase, and on cooling, two endothermic peaks can be seen at 111 ꢂC and
104 ꢂC confirming the nematic phase as well as SmA mesophase. On heating, decyloxy
homolog shows endothermic peak at 104 ꢂC indicates presence of nematic phase, and
on cooling, two endothermic peaks can be seen at 102 ꢂC and 99 ꢂC confirming the
nematic phase as well as SmA mesophase. On heating, dodecyloxy homolog shows
endothermic peak at 102 ꢂC indicates presence of nematic phase, and on cooling, two
endothermic peaks can be seen at 101 ꢂC and 89 ꢂC confirming the nematic phase as
well as SmA mesophase. On heating, tetradecyloxy homolog shows endothermic peak at
99 ꢂC indicates presence of nematic phase, and on cooling, two endothermic peaks can
be seen at 97 ꢂC and 95 ꢂC confirming the nematic phase as well as SmA mesophase.
On heating, hexadecyloxy homolog shows endothermic peak at 94 ꢂC indicates presence
of nematic phase, and on cooling, two endothermic peaks can be seen at 90 ꢂC and
88 ꢂC confirming the nematic phase as well as SmA mesophase. Reference to Table 3
shows that the mesophase length and thermal stabilities of Series I are 15 and 119 while

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
85
Table 3. The mesophase length, phase transition, and comparative molecular structure of n-hexyloxy
derivative of Series I and A.
Commencement
of smectic
A phase
Mesophase
range
Thermal
stabilities SmA-I
Commencement
of nematic phase
Series No.
Compound
I
A
C6
C6
(15)
14
119
134
C3
C1
C3
C14
Table 4. Result of antimicrobial activity of synthesized compounds.
Compound name
E. coli MTCC 443
Aureus MTCC 96
Name of organism
C12 tert-butyl recrystalized
700
400
200
240
700
400
200
240
E. coli, S. aureus
E. coli, S. aureus
E. coli, S. aureus
C18 tert-butyl recrystalized(F2)
C18 tert-butyl recrystalized(F1)
Standard amoxicillin & clavulanic acid
in Series A, the mesophase length and thermal stabilities of Series A is 14 and 134. In
Series I, the mesophase range exists as monotropy and the difference is of only 1 ꢂC,
respectively, while in Series A, the mesophase range exists as enantiotropy. Reference to
the molecular structure, both the compounds differ only at the central linkage. The
Series A has additional central (-CH ¼ N-) linkage whereas the Series I only central
ester (-COO-) linkage. Series I compounds are showing lower readings, and readings
exist as monotropy and mesophases exist as in heating as well as in cooling conditions
which are quite in close agreement with the DSC readings taken. Therefore, the smectic
and nematic mesophase range and thermal stability of present Series I can be explained
in terms of the polarizability of the molecule resulting from (-COO-) ester group in the
central linkage and terminal tert-butyl chain in Series I.
4. XRD analysis
In order to verify the results obtained from POM and DSC, we have performed XRD of
n-dodecyloxy (Series I) to confirm the structure of various phases present at transition
temperature. The XRD patterns at their transition temperature are shown in Figure 5.
The recorded pattern contains a sharp peak. The obtained reflection pattern [45] and
microscopic textural observations confirm the presence of nematic phase as well as
smectic phase.
5. In vitro antibacterial activity
A sensitivity analysis is a test that determines the sensitivity of bacteria to an antibiotic.
It also determines the ability of the drug or a compound to kill the bacteria.
Two compounds at different test concentrations were tested for its antibiotic proper-
ties or effect against gram-positive and gram-negative bacteria, namely E. coli MTCC
443 and S. aureus MTCC 96. Clavum (amoxicillin and clavunilic acid) was used as con-
trol standard in all the plates. Amoxicillin and clavunilic acid are used for the treatment
of many infections caused by bacteria. Amoxicillin inhibits the growth of bacteria.
Significant zone of inhibition could be observed for control standard in all the plates of

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S. THAKUR AND H. N. PATEL
Figure 5. Diffraction pattern graphics XRD pattern of compound C12-Series I at 102 ꢂC.
Figure 6. Antimicrobial activity at various concentrations with standard drug.
Figure 7. Zone of inhibition.
E. coli as well as S. aureus. None of test compounds showed zone of inhibition against
E. coli, and only n-dodecyloxy and n-octadecyloxy compounds showed inhibition zone
against S. aureus at two concentrations.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
87
From the above experiment, it can be concluded that compound n-dodecyloxy
showed zone of inhibition at minimum inhibitory concentration 700 (lg/ml) and com-
pound n-octadecyloxy showed zone of inhibition at 200 minimum inhibitory concentra-
tion (lg/ml), respectively, against S. aureus, whereas no compounds showed zone of
inhibition against E. coli. The zone of inhibition observed for two compounds against S.
aureus was less compared to control standard but satisfactory.
Conclusion
We have synthesized a homologous series with terminal tert-butyl and alkoxy side
chain. The presence of terminal tert-butyl group and the ester (-COO-) group at center
leads to have mesophases. The classical schlieren pattern of the nematic mesophase
commences as enantiotropy from n –propyloxy, and smectic A mesophase with focal
conic pattern commences as monotropy from n -propyloxy and persists up to the n-
octadecyloxy derivative of the series with great thermal stability. The methoxy and
ethoxy derivatives are non-mesogenic due to the presence of short alkyl spacer. The
mesogenic behavior was studied using POM, DSC, and XRD. Further, antimicrobial
activities of few compounds were performed, and results show that the derivatives may
be bioactive.
Acknowledgments
The authors are thankful to principal Dr. Keyur Shah, Shri M. M. Patel Institute of Sciences and
Research, Kadi Sarva Vishwavidhyalaya, Gandhinagar, Gujarat, for providing research facilities.
Dr. H. N. PATEL is thankful to GUJCOST (GUJCOST/MRP/2016-17/441) for the grant of minor
research project titled “Synthesis, Characterization and Mesomorphic Properties of Novel Liquid
Crystalline Materials.”
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