A comparative study of mesomorphism in symmetric and nonsymmetric dimers

Article abstract of DOI:10.1080/15421406.2014.939603

A homologous series consisting of 12 homologue symmetrical dimers, viz., bis(4-n-alkoxy benzoyloxy) 2,2-diphenyl propanes was synthesized, studied, and evaluated to establish the relation between molecular structure and mesomorphic properties on comparative basis with nonsymmectric dimers. The methoxy to pentyloxy homologue dimers, the novel symmetric series, are nonmesogenic. Mesomorphism commences from the hexyloxy homologue as smectic and nematic. The hexyloxy to decyloxy dimers possess smectogenic character with nematogenic character and the dodecyloxy to hexadecyloxy homologue dimers exhibit nematogenic character without the exhibition of smectogenic character. All the mesogenic homologues are enantiotropic mesomorphs. The smectic and nematic thermal stability of series is 129.0°C and 147.7°C, respectively, and mesomorphic phase length varies between 18°C for the hexadecyloxy homologue and 56°C for the heptyloxy homologue.

Full text of DOI:10.1080/15421406.2014.939603

This article was downloaded by: [Deakin University Library]
On: 15 March 2015, At: 02:52
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Molecular Crystals and Liquid Crystals
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/gmcl20
A Comparative Study of Mesomorphism
in Symmetric and Nonsymmetric Dimers
V. C. Kotadiyaa, M. D. Khunta & U. C. Bhoyaa
a Department of Chemistry, Saurashtra University, Rajkot, Gujarat,
India
Published online: 26 Feb 2015.
Click for updates
To cite this article: V. C. Kotadiya, M. D. Khunt & U. C. Bhoya (2015) A Comparative Study of
Mesomorphism in Symmetric and Nonsymmetric Dimers, Molecular Crystals and Liquid Crystals, 607:1,
135-143, DOI: 10.1080/15421406.2014.939603
To link to this article: http://dx.doi.org/10.1080/15421406.2014.939603
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or
howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &

Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

Mol. Cryst. Liq. Cryst., Vol. 607: pp. 135–143, 2015
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2014.939603
A Comparative Study of Mesomorphism
in Symmetric and Nonsymmetric Dimers
V. C. KOTADIYA, M. D. KHUNT, AND U. C. BHOYA∗
Department of Chemistry, Saurashtra University, Rajkot, Gujarat, India
A homologous series consisting of 12 homologue symmetrical dimers, viz., bis(4-n-
alkoxy benzoyloxy) 2,2-diphenyl propanes was synthesized, studied, and evaluated to
establish the relation between molecular structure and mesomorphic properties on com-
parative basis with nonsymmectric dimers. The methoxy to pentyloxy homologue dimers,
the novel symmetric series, are nonmesogenic. Mesomorphism commences from the
hexyloxy homologue as smectic and nematic. The hexyloxy to decyloxy dimers possess
smectogenic character with nematogenic character and the dodecyloxy to hexadecyloxy
homologue dimers exhibit nematogenic character without the exhibition of smectogenic
character. All the mesogenic homologues are enantiotropic mesomorphs. The smectic
and nematic thermal stability of series is 129.0◦C and 147.7◦C, respectively, and meso-
morphic phase length varies between 18◦C for the hexadecyloxy homologue and 56◦C
for the heptyloxy homologue.
Keywords Liquid crystal; mesomorphs; nematic; smectic; symmetrical dimers
Introduction
The molecules of mesogenic materials are geometrically constructed by linking two identi-
cal or unidentical units with a flexible spacer, generally a polymethylene unit [1, 2]. Dimers
consisting of two identical units are known as symmetric dimmers [3, 4]. The magnitudes
of molecular rigidity and flexibility [5–8] depend upon the number of phenyl rings, i.e.,
molecular aromaticity, length, polarity of flexible spacers, molecular polarizability, disper-
sion forces, etc., which [9, 10] contribute to the suitable magnitudes of anisotropic forces
of end to end as well as lateral to terminal intermolecular closeness and attractions required
to induce thermotropic mesomorphism [11], degree of mesomorphism, and the type of
mesomorphism. The present investigation is planned with a view to establishing and under-
standing the relation between molecular structure and mesomorphic tendency of a substance
[12]. The present novel investigation involves the synthesis of a novel homologous series of
symmetric dimers in which two identical units, viz., RO C6H4 COO C6H4 are bonded
to the middle carbon of propane (R CnH2n+1). The novel dimers are to be characterized
by elemental analysis, infrared, 1H NMR, and mass spectroscopy, and for mesomorphism
through an optical polarizing microscope equipped with a heating stage.
∗Address correspondence to U. C. Bhoya, Department of Chemistry, Saurashtra University,
Rajkot 360005, Gujarat, India, Tel: +91-9824203183; Fax: +0281-2583984. E-mail: drucbhoya@
gmail.com
Color versions of one or more of the figures in the article can be found online at
www.tandfonline.com/gmcl.
135

136
V. C. Kotadiya et al.
Experimental
Synthesis
4-n-Alkoxy benzoic acids were prepared by reacting 4-hydroxy benzoic acid and suitable
alkylating agent (R-X) in methanol in the presence of KOH by a modified method of Dave
and Vora [13]. The dimeric 4-n-alkoxy benzoic acids are individually converted to 4-n-
alkoxy acid chlorides by refluxing in an excess of thionyl chloride [14, 15] and then treated
with bis(4-hydroxy) 2,2-diphenyl propane (m.p. 158◦C) [16] in ice cooled pyridine [17].
Next day, the dimer formed was decomposed, filtered, washed, dried, and purified until
constant transition temperatures were obtained.
The chemicals required for synthesis are 4-hydroxy benzoic acid, methanol, KOH,
thionyl chloride, bis(4-hydroxy) 2,2-diphenyl propane, pyridine, and ethanol, and they
were used as received except solvents, which were dried, purified, and distilled prior to use.
The synthetic route to the series is shown in Scheme 1.
Characterization
The constitution of all the synthesized compounds has been characterized by ele-
1
mental analysis (Table 1), FT-IR and H NMR spectroscopy were further supported
Scheme 1. Synthetic route to the novel series.

Mesomorphism in Symmetric and Nonsymmetric Dimers
137
Table 1. Elemental analysis for (1) propyloxy, (2) hexayloxy, and (3) decyloxy derivatives
Elements % found Elements % calculated
Sr. no.
Molecular formula
C
H
O
C
H
O
1
2
3
C35H36O6
C41H48O6
C49H64O6
76.11
77.41
78.63
6.60
7.57
8.56
17.29
15.02
12.81
76.06
77.33
78.57
6.57
7.60
8.61
17.37
15.07
12.82
by mass spectroscopy. Purity of all the compounds has been checked on thin layer
chromatography. Elemental analyses were performed on EuroEA Elemental Analyzer
(Perkin-Elmer PE 2400 CHN Analyzer, Waltham, Massachusetts, U.S.A.). IR spec-
tra were recorded on Shimadzu FTIR-8400 (SHIMATZU FTIR-8400 Spectrophotome-
1
ter, Nishinokyou Kuwabara-cho, Nakagyo-Ku Kyoto, Japan), H NMR spectra were
recorded on BRUKER Avance-III (400 MHz) spectrometer (Bruker Spectrometer, Bil-
lerica, Massachusetts, U.S.A.) using CDCl3 as a solvent and mass spectra were recorded
on Shimadzu GC-MS Model No. QP-2010 (SHIMATZU GC-MS Model No. QP-2010,
Nishinokyou Kuwabara-cho, Nakagyo-Ku, Kyoto, Japan). The liquid crystal behavior
and the type of textures were determined by a miscibility method on microscopic
observations.
Analytical Data
Elemental analysis (see Table 1).
Spectral Data
1H NMR in ppm for Heptyloxy Derivative. 0.88 (t, 6H, CH3), 1.29–1.50 (m, 16H,
(CH2)4 ), 1.70 (m, 4H, CH2CH2O ), 1.71 (s, 6H, CH3 C(Ph)2 CH3), 4.03 (t, 4H,
OCH2), 6.99–7.12 (dd, 8H, Ar H), 7.29–8.01 (d, 8H, Ar H). The NMR data confirm
the molecular structure.
1H NMR in ppm for Tetradecyloxy Derivative. 0.87 (t, 6H, CH3), 1.25–1.48 (m, 44H,
(CH2)11 ), 1.75 (m, 4H, CH2CH2O ), 1.73 (s, 6H, CH3 C(Ph)2 CH3), 4.05 (t, 4H,
OCH2), 7.10–7.40 (dd, 12H, Ar H), 8.10 (d, 4H, Ar H). The NMR data confirm the
molecular structure.
IR in cm−1 for Butyloxy Derivative. 3075 (C H Str. of aromatic ring), 2839, 2986 (C H
Str. of polyethylene group), 1728 (C=O Str. of ester group), 1508, 1606 (C=C Str. of
aromatic ring), 1419 (aliphatic C H bend), 1066, 1170, 1271 (C O Str. of ester group),
842 (para substituted phenyl ring). The IR data are consistent with the molecular structure.
IR in cm−1 for Octyloxy Derivative. 2852, 2928 (C H Str. of polyethylene group), 1732
(C=O Str. of ester group), 1512, 1604 (C=C Str. of aromatic ring), 1429 (aliphatic C H
bend), 1062, 1165, 1257 (C O Str. of ester group), 844 (para substituted phenyl ring). The
IR data are consistent with the molecular structure.
Mass Spectra of Pentyloxy Derivative. m/z (rel. int%): 608 (M)+, 524, 418, 191, 121.
Mass Spectra of Ethyloxy Derivative. m/z (rel. int%): 524 (M)+, 149, 137, 121.

138
V. C. Kotadiya et al.
Results and Discussion
4-n-Alkoxy benzoic acids are dimeric and on linking it with bis(4-hydroxy) 2,2-diphenyl
propane through corresponding acid chloride yields novel symmetrical dimeric homo-
logues, which exhibit mesomorphic behavior from the hexyloxy dimer. Transition tem-
peratures (Table 2) were determined by an optical polarizing microscope equipped with
a heating stage. Nematogenic mesophase formation occurs from the hexyloxy to the hex-
adecyloxy homologues; but the hexyloxy, heptyloxy, octyloxy and decyloxy homologues
exhibit enantiotropically smectogenic mesophase formation in addition to the nematogenic
mesophase. The shorter homologues of methoxy to pentyloxy homologue failed to exhibit
mesomorphism even in the monotropic condition. A phase diagram (Fig. 1) showing meso-
genic phase behavior is plotted for the number of carbon atoms present in the n-alkyl chain
of left and right n-alkoxy terminal end groups versus transition temperatures. Transition
curves, viz., solid-isotropic/mesomorphic, smectic-nematic, and nematic-isotropic, are ob-
tained by joining like or related points. The solid-isotropic/mesomorphic transition curve
follows majorly a zigzag path of rising and falling values as the series is ascended and
behaves in a normal manner. The smectic-nematic transition curve initially rises and then
descends after passing through maxima at the octyloxy dimer; and behaves in a normal
established manner up to the decyloxy dimer and then, the curve ceases to appear for higher
homologue dimers. The nematic–isotropic transition curve is descended up to the decyloxy
homologue and behaves in a normal manner, but it deviates from normal behavior for the
higher dodecyloxy, tetradecyloxy, and hexadecyloxy derivatives. The smectic–nematic and
nematic–isotropic transition curves show an odd–even effect and an alternation of the tran-
sition temperatures. The odd–even effect diminishes for higher homologues. The transition
curves showing odd–even effects are extrapolated [18–20] to the lower odd (fifth) member
of the series to magnify the odd–even effect and to determine the smectic–nematic transi-
tion temperature of fifth member of the series. The smectic–nematic transition curve is also
extrapolated for the dodecyloxy dimer to predict its latent transition temperature (L. T. T.)
Table 2. Transition temperatures in ◦C of series 1
Transition temperature in ◦C
Compound no.
R = n-alkyl group CnH2n+1
Sm Nm isotropic
1
2
1
2
– – 226.0
– – 176.0
3
3
– – 140.0
4
4
– – 115.0
5
5
– – 130.0
6
7
8
9
10
11
12
6
7
8
10
12
14
16
106.0 128.0 160.0
114.0 146.0 170.0
116.0 150.0 166.0
80.0 92.0 108.0
– 126.0 150.0
– 101.0 120.0
– 142.0 160.0
Sm: Smectic, Nm: Nematic.

Mesomorphism in Symmetric and Nonsymmetric Dimers
139
Figure 1. Phase behavior of series.
for smectic, which is far below (64.0◦C) the solid-nematic transition temperature (126.0◦C).
The extrapolation of the transition curves is done by following the trend of the corresponding
transition curve [21]. Mesogenic properties from homologue to homologue in the present
series show variations due to the combined effect of molecular rigidity and flexibility.
Thus, the present novel series is predominantly nematogenic and partly smectogenic with
high melting type and wide degree of mesomorphism. The smectogenic mesophase length
varies between 12◦C and a maximum 34◦C at the octyloxy homologue and the nematogenic
mesophase length varies from a minimum of 18◦C at the hexadecyloxy homologue to a
maximum of 32◦C at the hexyloxy homologue. Thus, overall the mesogenic phase length
varies between 18◦C at the hexadecyloxy dimer and 56◦C at the heptyloxy derivative.
The smectic–nematic and nematic–isotropic thermal stabilities are 129.0◦C and 147.7◦C,
respectively.
Dimerization of 4-n-alkoxy benzoic acids disappears by breaking of hydrogen bonding
between two molecules by the process of esterification through corresponding acid chlo-
rides, yielding symmetric dimer as final product using the symmetrical phenolic component
of propane. The absence of mesogenic properties in first five homologues is attributed to
their high crystallizing tendencies, which arise from their inability to resist thermal vi-
brations due to inadequate quantum of mesophase thermal stabilization energy (enthalpy
ꢀH) as a consequence of unfavorable magnitudes of molecular rigidity and flexibility.
The exhibition of mesomorphism by the hexyloxy to hexadecyloxy dimers is attributed to
the suitable magnitudes of anisotropic forces of intermolecular closeness and end to end
and/or lateral attractions as a consequence of favorable magnitudes of molecular rigidity
and flexibility to maintain the disalignment of molecules at an angle less than 90◦ within
definite range of temperature on a floating surface. Thus, molecules of hexyloxy to decyloxy
dimers occupy a sliding layered ordered arrangement of molecules in floating condition
within a definite temperature range due to the presence of lamellar packing of molecules
in their original crystal lattices to form a smectic phase. Then the same four dimers show
a statistically parallel orientational order of molecules in a floating condition causing the

140
V. C. Kotadiya et al.
appearance of the nematic mesophase. However, the dodecyloxy, tetradecyloxy, and hex-
adecyloxy homologues due to the absence of lamellar packing of molecules in their crystal
lattices fail to exhibit smectogenic character in a floating condition, but maintain the statis-
tically parallel orientational order of molecules showing the exhibition of only nematogenic
character.
The changing mesomorphic behavior from homologue to homologue in the presently
investigated novel series is attributed to the sequentially and progressively added methy-
lene unit in the terminal chains. The odd–even effect for the smectic–nematic and
nematic–isotropic transition curves appears for a very small range of the correspond-
ing curve and from the sixth and seventh members of the series merges into the
main trend of the corresponding curves at the octyloxy derivative. The odd–even effect
disappears from and beyond the octyloxy homologue, because the longer chain may
coil, bend, flex, or couple with the major axis of the core. The extrapolation of the
smectic–nematic and nematic–isotropic transition curves for the pentyloxy homologue
predicts a nematic–isotropic and solid-nematic transition temperature of 170◦C and 130◦C,
respectively. The mesogenic properties of present series 1 are compared with structurally
similar homologue series X [22] as shown in Fig. 2.
The presently investigated novel dimer series 1 and structurally similar homologous
series X of dimers chosen for comparison are identical with respect to four phenyl rings,
which are contributing toward molecular linearity and rigidity. However, they differ with
respect to their symmetry character and the groups, linking the phenyl rings. The novel series
1 is symmetric, while series X is nonsymmetric. The linking groups of each section of the
dimers are different with two COO groups present in series 1 and two N=N groups
in series X. The central linking groups of C(CH3)2- and O (CH2)n
O
for series 1
and series X, respectively, are also different. Thus, the molecular changes obviously cause
variations in mesogenic properties and the degree of mesomorphism for series 1 and X. The
above variations between series 1 and X generate variations in combine effects of molecular
rigidity and flexibility and the suitable magnitudes of anisotropic forces of intermolecular
closeness and end to end as well as lateral attractions due to varying molecular polarity
and polarizability, types of symmetry, dispersion forces, polarity of –COO and N=N
group, location and number of methylene units in n-alkyl chain at the central place or at
the end of a molecule including effects due to unlike C6H13 and C2H5 end groups, etc.
O
O
RO
CH3
CH3
OR
Series-1
Series-X
O
O
R= CnH2n+1 Where, n=1to 8, 10, 12, 14, 16
N
N
N
N
C2H5
O (CH2)n O
C6H13
Where, n = 4,5,6,7,8,9,10,11,12
Figure 2. Structurally similar isomeric/nonisomeric series.

Mesomorphism in Symmetric and Nonsymmetric Dimers
141
• Symmetric homologous series 1 is smectogenic in addition to nematogenic (C6 C10)
and only nematogenic for C12, C14, and C16 homologues. At the same time, series X
is smectogenic in addition to nematogenic (C4 C9) and only nematogenic for C10,
C11, and C12.
• Odd–even effect is exhibited by transition curves of the phase diagram for
smectic–nematic and nematic–isotropic phase transformation by series 1 and X.
However, odd–even effect is relatively more pronounced for series X, than series 1.
• Addition of methylene unit at the n-alkyl chain of the middle central group and
terminal end group does not lengthen molecular length in equal magnitude and
affects unequally in thermal stability and transition temperatures behavior.
• Smectic and nematic thermal stabilities of series 1 are relatively lower than a series
X, facilitating mesophase stabilization and group efficiency order.
• Smectic in addition to nematic mesophase commences from sixth (C6) member of
a series 1; whereas it commences earlier by two homologues, i.e., from fourth (C4)
member of a series -X. Following Table 3 represents the average thermal stability
values for smectic and nematic mesophases.
• Total mesomorphic phase length for series 1 varies between 18◦C and 56◦C and that
of a series X, wonderfully varies between 18◦C and 58◦C.
Both the series (1 and X) under comparison are long and linear with differing features
and possess different magnitudes of anisotropic forces of intermolecular end to end and
lateral attractions as a consequence of their individually differing molecular rigidity and
flexibility. Both series show mesomorphic behavior as smectic and nematic type. The
thermal stability of presently investigated dimer series 1 is lower than that of series X for
the smectic and the nematic mesophases. The oxygen atom of the central carboxy group in
the molecule of series 1 will bump into the non-bonded sides of the adjacent hydrogens of the
aromatic ring, which will cause considerable strain on the molecule. Consequently, a twist
around C O bond will occur forcing the phenyl ring out of the plane of a molecule. Thus, the
coplanarity of the molecules is reduced to some extent making them thick. The central bridge
N=N certainly endows the molecules with coplanarity in trans position. On account of
these differences, the mesophase thermal stabilities (smectic and nematic) of series 1 are
in general way relatively lower than the corresponding mesophase (smectic and nematic)
thermal stabilities of a homologous series X. Moreover, early or late commencement of
smectic and nematic mesophase depends upon the extent of noncoplanarity caused by a
molecule. Thus, difference in molecular coplanarity causes commencement of smectic and
nematic mesophase earlier by two homologues (C4) in case of series X and a little bit late,
from sixth (C6) homologue in series 1. The addition of methylene unit simultaneously to the
Table 3. Average thermal stability in ◦C
Series→
Smectic—nematic
Commencement of
smectic phase
[1]
129.0
[C6 C10]
C6
[X]
139.5
[C4 C9]
C4
Nematic—isotropic
Commencement of
nematic phase
147.7
[C6 C16]
C6
152.7
[C4 C12]
C4

142
V. C. Kotadiya et al.
terminal group of series 1 and to the middle central group (CH2)n of series X does not
increase the molecular length in equal magnitudes, because n-alkyl chain in terminal group
of series 1 is bonded toward one side of a phenyl ring through oxygen atom, while n-alkyl
chain in middle central bridge is bonded toward both end side of the two phenyl rings
through two oxygen atoms. Therefore, n-alkyl chain bonded as terminal end group enjoys
relatively more flexibility in series 1 as compared to less flexibility enjoyed by n-alkyl chain
at the middle central position in case of series X. Thus, n-alkyl chain as terminal end group
can coil, bend, flex, or couple to lie with major axis of the core structure; but as middle
central group cannot. Thus, unequal increase in molecular length by adding methylene
unit causes variations in the molecular rigidity and flexibility. Hence, such variations are
reflected in the mesogenic properties between two same homologues of different series;
or series to series. Odd–even effect is more pronounced in series X as compared to series
1, because mesomorphism commences earlier from fourth (C4) homologue in series X
while it commences late from sixth (C6) homologue in series 1. Individual smectic and
nematic mesophase length differs for series 1 and X, but total mesophase length (smectic
+ nematic) varies between 18◦C and 56◦C as well as 18◦C and 58◦C for series 1 and series
X, respectively.
Conclusions
• A symmetric novel homologous series of dimers of propane derivatives with four
phenyl rings and symmetrically bonded two n-alkoxy terminal end groups as well
as two carboxy central groups synthesized and its mesomorphic properties are
compared with an unsymmetrical azoester homologous series bearing C2H5 and
C6H13 terminal end groups and O (CH2) n
second and third two phenyl rings out of four.
O
middle central group linking
• The group efficiency order derived on the basis of (i) thermal stabilities and (ii) early
commencement of mesophase for smectic and nematic are as under
(i) Smectic: unsymmetrical series X > symmetrical series 1
Nematic: unsymmetrical series X > symmetrical series 1
(ii) Smectic: unsymmetrical series X > symmetrical series 1
Nematic: unsymmetrical series X > symmetrical series 1
• Therefore, group efficiency order of,
• Middle central group of n-alkyl chain > terminal end group of n-alkyl chain
OR
O (CH)n
O
> CnH2n+1 O
• The individual smectic and nematic mesophase lengths differ between symmetric
and unsymmetric homologous dimer series but total mesophase length range remains
very closer. That is, addition of methylene unit to n-alkyl chain of either terminal
end group or to the middle central group of a dimer homologous series induces
total mesophase length range (Sm+Nm) almost equivalent irrespective of symmetry
(symmetric or nonsymmetric) of a dimer series, but individual mesophase length
range for smectic and/or nematic may alter.
• Molecular rigidity and flexibility are sensitive and susceptible to molecular structure
of a substance.

Mesomorphism in Symmetric and Nonsymmetric Dimers
143
• Suitable magnitudes of anisotropic forces of intermolecular attraction as a conse-
quence of favorable molecular rigidity and flexibility can induce mesomorphism.
• The novel series of dimers is predominantly nematogenic and partly smectogenic.
Acknowledgments
Authors acknowledge thanks to the Department of Chemistry (DST-FIST Funded & UGC-
SAP Sponsored) Saurashtra University, Rajkot, for research work. Authors are also thankful
to Dr. A. V. Doshi, Ex. Principal M.V.M. Science and Home Science College Rajkot, for
his valuable cooperation during present investigation as and when needed. Also thanks are
due to the National Facility for Drug Discovery through New Chemical Entities (NCEs),
for analysis of samples.
References
[1] Rahman, M. L., Asik, J., Kumar, S., Silong, S., & Rahman, M. Z. A. (2009). Phase Trans., 82,
228.
[2] Mossety-Leszczak, B., Galina, H., & Wlodarski, M. (2011). Phase Trans., 84, 15.
[3] Marcelis, A. T. M., Koudjs, A., Karczmarzuk, Z., & Sudholter, E. J. R. (2003). Liq. Cryst., 30,
1357.
[4] (a) Imrie, C. T., & Henderson, P. A. (2007). Chem. Soc. Rev., 36, 2096. (b) Demus, D., Goodby, J.,
Gray, G. W., Spiess, H. W., & Vill, V. (Eds.) Handbook of Liquid Crystals. (1998). Wiley-VCH:
Weinheim, pp. 801–833.
[5] Marcos, M., Lomenta, A., Serrano, J. L., & Ezcurra, A. (1992). Adv. Mater., 4, 285.
[6] Hird, M., Toyne, K. J., & Gray, G. W. (1993). Liq. Cryst., 14, 741.
[7] Hird, M., Toyne, K. J., Gray, G. W., Day, S. E., & Mc Donnell, D. G. (1993). Liq. Cryst., 15,
123.
[8] Gonzales, Y., Ros, M. B., Serrano, J. L., & Pereziubind, A. (1998). Liq. Cryst., 18, 751.
[9] Gray, G. W., & Windsor, P. A. (1974). Liquid Crystals and Plastic Crystals, Vol. 1., Ellis
Horwood: Chichester: Ralsted Press. A Division of John Wiley and Sons, Inc.: New York,
London, U.K., pp. 327–356, chapter 4.
[10] Gray, G. W. (1962). Molecular Structure and Properties of Liquid Crystals. Academic Press:
London.
[11] (a) Demls, D. (1988). Mol. Cryst. Liq. Cryst., 165, 45. (b) Demls, D. (1989). Liq. Cryst., 5, 75.
[12] Gray, G. W. (1979). Liquid Crystal and Molecular Structure-Nematic and cholesterics, in The
Molecular Physics of Liquid Crystals, G. R. Luckhurst and G. W. Gray, eds, Academic Press:
London, pp. 1–30.
[13] Dave, J. S., & Vora, R. A. (1970). In: Liquid Crystal and Ordered Fluids, Johnson, J. F. & Porter
R. S. (Eds.), Plenum Press: New York, 477 pp.
[14] Bhoya, U. C., & Doshi, A. V. (2000). J. Inst. Chem. (India), 72, 15.
[15] Suthar, D. M., & Doshi, A. V. (2012). Mol. Cryst. Liq. Cryst., 569, 64.
[16] (a) Dianin, A. P. (1891). Z. Russkogo Fiziko-Khimicheskogo Obshchestva, 23, 492. (b) Zincke,
T. (1905). Justus Liebigs Ann. Chem., 343, 75.
[17] Doshi, A. V., & Ganatra, K. J. (1999). Proc. Ind. Acad. Sci. (Chem. Sci.), 4, 563.
[18] Travadi, J. J., Bhoya, U. C., & Doshi, A. V. (2012). Mol. Cryst. Liq. Cryst., 552, 10.
[19] Ganatra, K. J., & Doshi, A. V. (2000). J. Inst. Chem. (Ind.), 72, 61.
[20] Doshi, A. V., & Lohar, J. M. (1993), Ind. Acad. Sci. Chem. Sci., 105, 209.
[21] Bhoya, U. C., Vyas, N. N., & Doshi, A. V. (2012). Mol. Cryst. Liq. Cryst., 552, 104.
[22] Blatch, A. E., & Luckhurst, G. R. (2000). Liq. Cryst., 27, 775.