Study of the molecular structure on liquid crystal properties with reference to thermotropic azoester derivatives

Article abstract of DOI:10.1080/15421406.2016.1262681

An azoester homologues series: RO?C₆H₄?COO?C₁₀H₆?N?N?C₆H₄?OC₅H₁₁ (para) as novel liquid crystalline (LC) materials has been synthesized and studied with a view to understanding and establishing the effects of molecular structure on LC properties with reference to laterally substituted phenyl ring and terminally substituted ?OR and ?OC₅H₁₁ (n) groups; including ?COO? and ?N?N? central bridges. Novel homologous series of thermotropic LC variety consists of thirteen homologues (C₁ to C₁₈). C₁ to C₃ derivatives are nonliquid crystal (NLC); C₄ is only nematogenic and C₅ to C₁₈ are smectogenic plus nematogenic. All the mesogenic homologues (C₄ to C₁₈) are enantiotropically nematogenic or/and smectogenic as confirmed by a polarizing optical microscopy (POM) equipped with a heating stage. Transition curves Cr-I/M, Sm?N, and N?I behaved in normal manner in a phase diagram. Odd-even effect is exhibited by Sm?N and N?I transition curves. Analytical, spectral and thermal data confirms the molecular structure of novel homologues. Novel azoester series is predominantly nematogenic and partly smectogenic whose mesogenic temperatures ranges minimum to maximum from 79.0°C to 162.0°C. Thermal stability for smectic and nematic are 128.2°C and 147.7 °C, respectively. Thus, it is a middle ordered melting type of novel series whose total mesophaselength ranges from 20.0°C to 56.0°C. Textures of nematic are threaded or schlieren and that of smectic are smectic A or C.

Full text of DOI:10.1080/15421406.2016.1262681

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Study of the molecular structure on liquid crystal
properties with reference to thermotropic
azoester derivatives
Vinay S. Sharma, U. H. Jadeja & R. B. Patel
To cite this article: Vinay S. Sharma, U. H. Jadeja & R. B. Patel (2017) Study of the molecular
structure on liquid crystal properties with reference to thermotropic azoester derivatives, Molecular
Crystals and Liquid Crystals, 643:1, 28-39, DOI: 10.1080/15421406.2016.1262681
To link to this article: http://dx.doi.org/10.1080/15421406.2016.1262681
Published online: 23 Feb 2017.
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Date: 24 February 2017, At: 12:01

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
http://dx.doi.org/./..
Study of the molecular structure on liquid crystal properties
with reference to thermotropic azoester derivatives
Vinay S. Sharma, U. H. Jadeja, and R. B. Patel
Chemistry Department, K. K. Shah Jarodwala Maninagar Science College, Gujarat University, Ahmedabad,
Gujarat, India
ABSTRACT
KEYWORDS
Azoester; nematic;
mesomorphism; smectic;
thermotropic
–
–
–
– = –
–
An azoester homologues series: RO C6H4 COO C10H6 N N C6H4
OC5H11 (para) as novel liquid crystalline (LC) materials has been synthe-
sized and studied with a view to understanding and establishing the
effects of molecular structure on LC properties with reference to later-
–
–
ally substituted phenyl ring and terminally substituted OR and OC5H11
–
–
– = –
(n) groups; including COO and N N central bridges. Novel homol-
ogous series of thermotropic LC variety consists of thirteen homologues
(C1 to C18). C1 to C3 derivatives are nonliquid crystal (NLC); C4 is only
nematogenic and C5 to C18 are smectogenic plus nematogenic. All the
mesogenic homologues (C4 to C18) are enantiotropically nematogenic
or/and smectogenic as confirmed by a polarizing optical microscopy
–
(POM) equipped with a heating stage. Transition curves Cr-I/M, Sm N,
and N I behaved in normal manner in a phase diagram. Odd-even effect
–
–
–
is exhibited by Sm N and N I transition curves. Analytical, spectral and
thermal data confirms the molecular structure of novel homologues.
Novel azoester series is predominantly nematogenic and partly smec-
togenic whose mesogenic temperatures ranges minimum to maximum
from 79.0°C to 162.0°C. Thermal stability for smectic and nematic are
128.2°C and 147.7 °C, respectively. Thus, it is a middle ordered melting
type of novel series whose total mesophaselength ranges from 20.0°C to
56.0°C. Textures of nematic are threaded or schlieren and that of smectic
are smectic A or C.
Introduction
An unique physical state of matter termed as liquid crystal (LC) or mesomorphic state [1]
which is neither fully crystalline nor fully isotropic liquid are useful in the manufacture of
electronic display devices, light emitting materials. Azoester dyes are equally useful as normal
dyes including changing their colors with changing frequency of exposed light. LC materials
are useful in pharma industry also [2–8]. However, present investigation is planned with a
view to understand and establish the effect of molecular structure [9–13] on LC property with
–
reference to tailed ended and left n-alkoxy terminal ended ( OR) groups excluding the study
of application part. Knowledge of predicting temperature range of LC state useful in desired
application, which is a basic fundamental knowledge of LC chemistry. Proposed investiga-
tion will consist of synthesis of a homologous series of two phenyl rings and one napthyl
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

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
29
ring linked through two central bridges and varying n-alkoxy left terminal group and fixed
–
n OC5H11 (para) tailed group. Behavior of LC state trend will be observed from homologue
to homologue in the same series and for the same homologue from series to series by compar-
ing with other structurally similar series. Evaluated results will be interpreted and discussed in
terms of molecular rigidity and flexibility [14–17]. Number of homologous series are reported
till the date [18–22].
Experimental
Synthesis
4-Hydroxy benzoic acid was alkylated using suitable alkylating agent (R-X) to convert it into
4-n-alkoxy benzoic acids (A) by modified method of Dave and Vora [23], Alkylation of Parac-
–
etamol using alkylating agent n C5H11Br is carried out to form 4-n-Pentyloxy acetanilide,
which on hydrolysis converted to 4-n-pentyloxy aniline which is formed by usual establish
method. Azo dye (B) 4-hydroxy benzoyloxy naphthyl azo 4ꢀ-pentyloxy benzene (m.p. 124°C,
yield 79%) was prepared by well-known azotization method [24]. Final azoester products
were synthesized by condensation of (A) and (B) [25]. Thus, the azo-ester homologue deriva-
tives were filtered, washed with sodium bicarbonate solution followed by distilled water, dried
and purified till constant transition temperatures obtained using an optical polarizing micro-
scope equipped with a heating stage. 4-Hydroxy benzoic acid, Alkyl halides, Paracetamol,
–
1 Napthol, dicyclohexyl carbodimide (DCC), dimethyl amino pyridine (DMAP), K2CO3,
NaOH, NaHCO3, NaNO2, KOH, DCM, MeOH, required for synthesis were used as received
except solvents which were dried and distilled prior to use. The synthetic route to the series
is mentioned in Scheme 1.
Characterization
Representative homologues of a series were characterized by elemental analysis, infrared spec-
1
1
troscopy, H NMR spectra. IR spectra were recorded on Perkin-Elmer spectrum GX, H
NMR spectra were recorded on Bruker using CDCl3 as solvent. Microanalysis was performed
on Perkin-Elmer PE 2400 CHN analyzer (Table 1). Texture image of some homologues for
nematic phase were determined by miscibility method (Table 2). Decomposition temper-
atures (Fig. 1) and the value of enthalpy and entropy (Table 3) were determined using of
Shimadzu DSC 60 differential Scanning Calorimeter with a heating rate of 5–10.0°C min−1.
Thermodynamic quantities enthalpy (ꢀH) and entropy (ꢀS = ꢀH/T) are qualitatively dis-
cussed. Transition temperatures (Table 4), Phase diagram (Fig. 2) and textures image (Fig. 3)
were determined using a polarizing optical microscopy (POM) equipped with heating stage
and digital camera. The phase sequence of C12 homologue during cooled condition given in
(Fig. 4). X-ray diffraction (XRD) were performed on a (X’ PERT MPD) makes Philips.
Analytical data
IR Spectra (KBr) in cm−1 for hexyloxy (C6), hexadecyloxy (C16), heptyloxy (C7),
derivatives
–
–
–
–
Hexyloxy: 761 Poly methylene ( CH2 )n of OC6H13, 885(−C–H– def. di-substituted-
–
–
Para), 690 Polymethylene ( CH2 ) of OC6H13, 989 (−C–H– def. hydrocarbon), 1060 and

30
V. S. SHARMA ET AL.
Scheme . Synthetic route to the series .
Table . Elemental analysis for ethoxy, propyloxy, butyloxy, hexyloxy, heptyloxy, and octyloxy derivatives.
%Elements found
H
%Elements calculated
H
Sr. no.
Molecular formula
C
N
C
N

CHON
CHON
CHON
HON
CHON
CHON
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%
.%





C
Table . Texture of nematic and smectic phase of C, C, C, C by miscibility method.
Sr. no.
Homologue
Texture




C
C
C
C
Threaded Nematic
Smectic-A
Schlieren Nematic
Threaded Nematic

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
31
Figure . DSC thermogram of C, C, C homologue.
– – –
– –
–
–
1105( C O ) Str, 1296 and 1321 and 1423, 1494 ( C O str in –(CH2 )n chain), 1579 ( C–
– = –
–
–
–
H– def. in CH2), 1390 ( N N )str, 1641 ( C = O group), 1735 ( COO ester group), 2870
–
and 3072 and ( C–H str in CH3). IR confirms the molecular structure.
–
–
–
Hexadecyloxy: 759 and 796 Polymethylene ( CH2 )n of OC16H33, 883(−C–H– def.
– – –
m di-substituted-Para), 989 (−C–H– def. hydrocarbon), 1008, 1056, ( C O ) Str, of
–
– –
–
–
OC5H11,1276 and 1392 and 1373, 1246( C O str in –(CH2)n chain, 1496( C–H– def. in
– = –
–
–
CH2),1512 and 1392 ( N N )str, 1598 ( C = O group), 1737 ( COO ester group), 2733
–
and 2916 and 3084 ( C–H str in CH3). IR confirms the molecular structure.
–
–
–
Heptyloxy: 761 Poly methylene ( CH2 )n of OC7H15, 885(−C–H– def. di-substituted-
–
–
–
Para), 690 Polymethylene ( CH2 ) of OC5H11, 989 (−C–H– def. hydrocarbon), 1060 and
– – – – –
–
–
1105( C O ) Str, 1296 and 1321 and 1423, 1494 ( C O str in –(CH2 )n chain), 1579 ( C–
– = –
–
–
–
H– def. in CH2), 1390 ( N N )str, 1660 ( C = O group), 1735 ( COO ester group), 2870
–
and 3072 and ( C–H str in CH3). IR confirms the molecular structure.
Table . Transition temperature (°C) and enthalpy (J g−) and entropy change (J g−k−) by DSC
measurement.
Homologues
or comp.
Heating
scan (°C)
Cooling
scan (°C)
ꢀH
ꢀH
ꢀS
ꢀS
Transition
(Jg−
)
(Jg−
)
(J g−k−
)
(J g−k−
)
C14
C18
C12
C16
Cr-SmC






















.
.
—
.
.
—
.
.
—
.
.
—
.
.
—
.
.
—
.
.
—
.
.
—
.
.
—
.
.
—
.
.
—
.
.
—
.
.
—
.
.
—
.
.
—
.
.
—
–
SmC N
–
N I
Cr-SmC
–
SmC N
–
N I
Cr-SmC
–
SmC N
–
N I
Cr-SmC
–
SmC N


–
N I

32
V. S. SHARMA ET AL.
Table . Transition temperature in °C for series-.
4ꢀ-n-alkoxy benzoyloxy-naphthylazo-4ꢀꢀ-pentyloxy benzene
Transition temperatures in ˚C
Compound no.
n-Alkyl chain CnHn+
Smectic
Nematic
Isotropic













C
C
C
C
C
C
C
C
C
C
C
C
C
—
—
—
—
—
—
.
.
.
.
.
.
.
.
.
.
.
.
.
—
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
1H NMR spectra in CDCl3 in δ ppm for tetradecyloxy and octyloxy derivative
–
–
Tetradecyloxy: 0.90(t, 6H, of OC5H11 and OC14H29), 1.31–1.39 (m, n-poly methylene
–
–
groups of OC14H29), 1.28–1.41 (m, n-poly methylene groups of OC5H11), 1.76(p, 10H,
OC14H29 and OC5H11), 4.06 (t, 6H, O CH2 CH2 of OC14H29 and OC5H11), 7.19
–
–
– –
–
–
–
–
and 7.89(d, 4H, p-disubstituted third phenyl ring), 7.08 and 8.24 (d, 4H, p-di substituted first
phenyl ring), 6.84 and 8.73, 8.21, 7.61 and 7.58 (d, 6H of middle ring), NMR confirms the
molecular structure.
Figure . Phase behavior of series.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
33
Figure . (a) Schlieren type texture of nematic phase of comp. C, (b) Sm A phase of comp.C, (c) Sm C phase
of comp. C (d) Threaded type image of nematic phase for comp. C.
–
–
–
Octyloxy: 0.90(t, 6H, of OC8H17 and OC5H11), 1.35–1.39 (m, n-poly methylene groups
–
–
– –
–
–
–
of OC5H11),1.76(p, 10H, OC8H17 and OC5H11), 4.08 (t, 6H, O CH2 CH2 of OC8H17
–
and OC5H11), 7.20 and 7.89 (d, 4H, p-disubstituted third phenyl ring), 7.12 and 8.19 (d, 4H,
p-di substituted first phenyl ring), 6.83 and 8.71, 8.21, 7.61 and 7.58 (d, 6H of middle ring),
NMR confirms the molecular structure.
Figure . Phase sequence of C homologue on cooled condition (a) isotropic at °C, (b) nematic phase at
°C, (c) smectic phase starts at °C, (d) cooled at °C, (e) formation of solid crystal.

34
V. S. SHARMA ET AL.
–
–
–
Butyloxy: 0.90(t, 6H, of OC4H9 and OC5H11), 1.31–1.39 (m, n-poly methylene groups
–
–
– –
–
–
–
of OC5H11),1.76(p, 10H, OC4H9 and OC5H11), 4.06 (t, 6H, O CH2 CH2 of OC4H9
–
and OC5H11), 7.19 and 7.89(d, 4H, p-disubstituted third phenyl ring), 7.10 and 8.19 (d, 4H,
p-di substituted first phenyl ring), 6.83 and 8.71, 8.21, 7.61, and 7.58 (d, 6H of middle ring),
NMR confirms the molecular structure.
–
–
–
–
Hexyloxy: 0.89(t, 6H, CH2 CH3, OC5H11 and OC6H13), 1.31–1.39 (m, n-poly methy-
–
–
lene groups of OC5H11), 1.29–1.41 (m, n-poly methylene groups of OC6H13), 1.76 (p,10H,
CH2 CH2 of OC5H11 and OC6H13), 4.06 (t, 6H, of OC5H11 and OC6H13), 7.19 and
–
–
–
–
–
–
–
7.83 (d, 4H, p-disubstituted third phenyl ring), 7.12 and 8.19 (d, 4H, p-di substituted first
phenyl ring). 6.83 and 8.71, 8.21, 7.61, and 7.58 (d, 6H of middle ring), NMR confirms the
molecular structure.
DSC analysis
In Fig. 1, shows the DSC results of comp. C14, C12, C18. The thermogram show firstly at
heating stage result an endothermic peak at 100°C (C14), 110°C (C12), and 80°C (C18). The
corresponding enthalpy change (ꢀH) was approximately 51.0 J/g (C14), 48.0 J/g (C12), and
38.2 J/g (C18). The second endothermic peak occurred at 133°C (C14), 131°C (C12), 110°C
(C18), and the enthalpy change (ꢀH) was 10.6 J/g (C14), 6.6 J/g (C12), and 7.2 J/g (C18).
During cooling condition, two exothermic peaks were observed, in the compound C14 at
94°C and 130°C, for compound C12 at cooling the two peaks observed at 88°C and 128°C,
respectively. Comp. C18 at cooling condition the peaks observed at 70°C and 108°C. The
mesophase is obtained and also confirmed by the POM investigation.
POM investigation
XRD measurements
To confirm the smectic phase, we performed the powder X-ray diffraction pattern (PXRD)
of compound C12 and C14 homologue, which was performed at nearly transition temperature
101°C shown in (Fig. 5). Low angle broad peak at (2θ = 3–5ꢀꢀ), and mid angle region at (2θ =
6–8ꢀꢀ) and d-spacing of the reflections observed at 9.2, 8.1, 1.1. For comp. C14, broad peak
observed at (2θ = 3–5ꢀꢀ), mid region at (2θ = 6–10ꢀꢀ), the d-spacing of the reflections observed
at 10.2, 9.8, and 1.2. No any other significant peaks at higher angles in present series. Due to
– = –
longer chain at n-alkoxy side chain and linearity of molecule with azo ( N N ) as a central
linkage and increases the stability of smectic phase. The reflections for the small angle area
Figure . X-ray diffractogram of compound C and C.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
35
Figure . Proposed molecular packing of the Sm C phase in present series.
indicates the presence of smectic phase. The proposed molecular packing of smectic C phase
in present synthesized newly homologues series are shown in (Fig. 6).
Result and discussion
Azo dye 4-Hydroxy benzoyloxy napthyl azo-4ꢀ-n-pentyloxy benzene (m.p. 124.0°C,
yield. 79%) is a nonmesomorphic component which, on condensation with 4-n-Alkoxy
benzoic acids yielded azoesters derivatives which exhibited mesomorphism from C4 to C18
homologues. Mesogenic homologues are smectogenic plus nematogenic expect C4 mem-
ber of a series. Transition and melting temperatures were determined by polarizing optical
–
–
microscopy (POM) equipped with a heating stage. Transition curves Cr-I/M, Sm N, and N I
are plotted for the number of carbon atoms present in n-alkyl chain versus transition temper-
atures (Table 4) by linking like or related transition points; as depicted in a phase diagrams
(Fig. 2). Cr-I/M transition curve rises and then falls in zigzag manner with overall descending
–
–
tendency and behaved in normal manner. Sm N and N I transition curves initially rises and
then descended as series is ascended with exhibition of odd-even effect up to C9 homologue
–
–
and behaved in normal established manner. Sm N and N I transition curves for odd and
even homologues are merging at C9 derivative, beyond which both transition curves propa-
gated as a single transition curve for higher homologues of longer n-alkyl (-R) chain. Ther-
mal stabilities for smectic and nematic are 128.2 and 147.7, respectively whose smectogenic
and nematogenic mesophaselengths are ranging between 17–36°C and 14–22°C, respectively.
The total mesophaselengths are varied between 20°C and 56°C at C4 and C7/C10 homologues.
Thermal, analytical, spectral and other experimental data supported the molecular structures
of novel homologues. Textures of mesophases of some homologues are confirmed by miscibil-
ity method; using POM. Sm N and N I transition curves are extrapolated to nonmesogenic
homologues to determine their latent transition temperatures (LTT) for smectic and nematic
mesophase formation. None of the mesogenic homologues are practically monotropic smectic
or/and nematic. The mesogenic properties and their magnitudes are varying from homologue
to homologue in the same series.
–
–
Nonmesomorphic component azo dye, on reacting with 4-n-alkoxy benzoic acids through
corresponding acid to induce mesomorphism (C4 to C18) except C1, C2, C3 homologue
derivatives and lowers the transition temperatures as compared to corresponding dimerized

36
V. S. SHARMA ET AL.
n-alkoxy acids. Lowering of transition temperatures are due to the breaking of hydrogen
bonding by esterification process between the two molecules of n-Alkoxy acid. The exhibition
of mesomorphism commencing from C4 homologue of present novel series is attributed to
the disalignment of molecules of mesogenic derivatives at an angle ninety (perpendicular)
or/and less than ninety degree to the plane of a floating surface as a consequence of increasing
molecular flexibility and constant molecular rigidity of suitable magnitudes to induce and
stabilize mesomorphism either as smectic plus nematic or as only nematic by arranging
molecules with stastically parallel orientational order or/and with sliding layered molecular
arrangement under floating condition, due to increase in the molecular length or size or
breadth, suitable length to breadth ratio, the ratio of the molecular polarity to polarizability,
intermolecular dispersion forces, dipole–dipole interactions, permanent dipolemoment
across the long molecular axis, etc. which are varying from homologue to homologue in
the same series, which resists externally exposed thermal vibrations and stabilizes smectic
and/or nematic phase for definite range of temperature. The nonmesomorphicity of C1, C2,
C3 homologue is attributed to the low magnitudes of intermolecular dispersion forces and
low magnitudes of dipole–dipole interactions leading to high crystallizing tendency which,
causes abrupt breaking of crystal lattices due to unsuitable and unfavorable magnitudes of
anisotropic forces of intermolecular attractions. Thus, irregular breaking of crystal lattices,
suddenly takes place, relatively at higher temperature, directly from crystalline solid state to
isotropic liquid state without passing through LC state.
The transition curves for smectic and nematic are extrapolated to nonmesomorphic homo-
logues C4, C3, and C2 to determine and predict their LTTs [26–29] but practically they are
unable to exhibit either of the mesophase or mesophases due to their high crystallizing ten-
dencies. All molecules of every homologues under exposed thermal vibrations from and
beyond isotropic temperature, randomly orient in all the possible directions with high order
of disorder or high entropy, but, on cooling the same from and below isotropic temperature
exhibited mesomorphism except C1, C2, C3 in reversible manner exactly at a temperature at
which mesophase was appeared on heating them. Therefore, their transition temperatures
were termed as enantiotropic transition temperatures. The exhibition of odd-even effect is
–
–
–
observed due to changing number of CH2 unit of n-alkyl chain ‘R’ of OR group for odd
and even numbered carbon atoms at the left terminal. The disappearance of odd-even effect
–
from and beyond C9 homologue of higher homologues of longer n-alkyl chain R of OR ter-
minal group is attributed to the coiling or bending or flexing or coupling of longer n-alkyl
–
chain ‘R’ or OR group which causes uncertainty in its status, affecting molecular rigidity
and/or flexibility which may result into deviating trend of a transition curve or may induce
more or less or negligible abnormality. The changing trend in mesogenic properties or behav-
iors from homologue to homologue in the same series is attributed to the variations in number
of carbon atoms which gradually vary, keeping rest of the molecular part unchanged. Thus,
suitable magnitudes of intermolecular anisotropic forces or dispersion forces are changing
with changing molecular polarity and polarizability.
The variations in mesogenic properties or behaviors of presently investigated novel series-
1 are compared with structurally similar analogous series X [30] and Y [31] as mentioned
below in (Fig. 7).
Above homologous series commonly consisted of two (first and last) phenyl rings and one
–
–
– = –
napthyl ring linked through COO as well as N N as central bridges in series-1 and X,
–
which constituted total molecular rigidity. Flexible group OR is also commonly present but
it varies from C1 to C18 homologue contributing partly to the total molecular flexibility. The
–
–
–
tail ended OC5H11(n), OC7H15 (n), and OC4H9 (n) are varying from series to series for

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
37
Figure . Structurally similar analogous series.
the same homologue causing difference to the value of total molecular flexibility for the same
–
homologue, keeping total molecular rigidity unaltered expert series-X. The OR group at the
left causes variation in total molecular flexibility from homologue to homologue in the same
series but contributes equally to the molecular flexibility for the same homologue from series
to series. Therefore, total molecular flexibility of all the individual homologues of all the series-
1, X and Y for the same homologue from series to series and from homologue to homologue
in the same series, including identical molecular rigidity are different to more or less extent
in their effective magnitudes. Thus, mesogenic properties and their degree of mesomorphism
will depend upon the differing features of analogous homologous series 1, X and Y. Some
physical thermometric properties are mentioned below in (Table 5) for the analogue series
under comparative study.
From above Table 5, it is clear that,
r
Thermal stabilities for smectic and nematic decreases from series 1 to Y to X, i.e., tailed
ended flexible groups OC5H11 (n) > OC4H9 (n) > OC7H15(n).
–
–
–
r
r
Early commencement of smectic and nematic mesophases are in decreasing order from
–
–
–
series 1 to series X to series Y or OC5H11 (n) > OC7H15 (n) > OC4H9 (n).
Upper total mesophaselengths increases from series-Y to series-X to series-1. i.e.,
–
–
–
–
–
OC5H11 (n) > OC7H15 (n) > OC4H9 (n) and lower total mesophase lengths are
–
decreasing from OC7H15 (n) > OC5H11 (n) > OC4H9 (n) or series-Y < series-1 <
series-X.
r
Odd members transition curve occupied lower positions than even members transition
curve.
Table . Thermal stabilities in°C.
Series→
–
–
–
Series- OCH (n)
Series-X OCH(n)
Series-Y OCH(n)
–
Sm-I or Sm N
.
.
.
–
–
–
Commencement of Smectic phase
(C C)
(C C)
(C C)
C
.
C
.
C
.
Nematic-Isotropic
–
–
–
Commencement of Nematic phase
(C C)
(C C)
(C C)
C
C
C
Total mesophase length in°C
.°C to .°C
C C/C
.°C to .°C
C C
.°C to .°C
C C

38
V. S. SHARMA ET AL.
An exhibition of smectic and nematic phase by all the homologue series 1, X and Y under
comparison are due to the suitable magnitudes of anisotropic forces of intermolecular cohe-
sions and closeness as a consequence of favorable magnitudes of molecular rigidity and flex-
ibility. But, their commencement of mesophase or mesophases, thermal stability, degrees of
mesomorphism and many other properties etc. differs with minor or major differences in their
mutual appearance of molecular structures for the same homologue from series to series and
homologue to homologue in the same series, e.g., Homologous series 1 and X differs by two
–
–
–
–
CH2 unit as well as series 1 and Y by one CH2 unit for the same homologue with respect
–
–
to tailed ended terminal end group. The differences in CH2 unit or units in terminal end
groups causes differences in molecular flexibility irrespective of their identical rigidity for the
same homologue from series to series. Therefore, their suitable magnitudes of intermolecular
anisotropic forces which resist exposed thermal vibrations under floating condition to facili-
tate and stabilize mesophase or mesophases for definite range of temperature which may differ
for the same homologue from series to series. The decreasing order of thermal stability for
–
–
smectic and nematic is observed for the series under comparison as OC5H11 (n) > OC4H9
(n) > OC7H15(n). It suggests that, lower n-alkoxy tail ended groups are normally bear higher
–
thermal stability than higher n-alkoxy tail ended group, i.e., lengthening of tail ended n-alkoxy
end group can reduce thermal stabilities. The early or late commencement of mesomorphism
–
depend upon the extent of molecular noncoplanarity. The tailed ended OC7H15 (n) and
–
–
OC5H11 (n) consists of odd numbered carbon whereas OC4H9 (n) is made up of even num-
bered carbon. Therefore, the type of functional group at the tailed end or the odd or even num-
ber of carbon atoms in n-alkoxy tailed ended group for the same homologue play an important
–
role in the extent of molecular noncoplanarity. Thus, even numbered (C4), i.e., OC4H9 (n)
group containing tailed ended group show commencement late whereas odd numbered
–
–
tail ended OC5H11 (n) and OC7H15 (n) group may result into early commencement of
mesophase.
Conclusion
r
Novel azoester homologous series is smectogenic in addition to nematogenic with lower
middle order melting type and behaves in normal established manner.
Mesomorphic tendency of a molecule depends upon suitable magnitudes of anisotropic
forces of intermolecular attractions and closeness as a consequence of molecular rigidity
and flexibility as immerged from molecular structure.
Molecular structure is very sensitive and susceptible to a phenomenon of mesomor-
phism.
Tailed ended n-alkoxy group can induce mesomorphism in an azoester homologous
series.
r
r
r
r
LC devices, light emitting materials, LC dye as coating materials are as equal as normal
dye, which, changes their colors with intensity of light. LC devices consumed 100 times
less electricity than conventional electric devices through reflected light.
r
Present study supported and raised the credibility to the conclusions drawn earlier.
Acknowledgments
Authors acknowledge thanks to Dr. R. R. Shah, principal of K. K. Shah Jarodwala Maninagar Science
College, Ahmedabad. Authors are thankful to Dr. A. V. Doshi, Ex-principal of M.V.M. Science and

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
39
Home Sci. College - Rajkot for his constant support, inspirations, valuable comments, suggestions, and
help, as and when needed during the course of present investigation. Authors Acknowledge thanks to
NFDD Centre for the analytical and spectral services.
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