Tuning the thermotropic properties of liquid crystalline p-substituted aroylhydrazones

Article abstract of DOI:10.1039/c5ra06620d

The synthesis and mesomorphic properties of forty substituted aroylhydrazones with peripheral mono-, di- and tri- alkoxy chains derived from a p-amino aroylhydrazone core are described. The compounds with two side chains exhibited a smectic A phase, while the compounds with six soft alkoxy side chains at symmetrical positions formed a rectangular columnar mesophase. The structures of these mesophases were confirmed by differential scanning calorimetry (DSC) analysis, polarized optical microscopy (POM) and powder X-ray diffraction (XRD) studies. Raman studies with the help of density functional theory on some of the mesogenic members have been performed to understand the changes in the intermolecular interactions during phase transitions. A structure-property relationship has been deduced, and mesogenic properties are found to be dependent on the chain length, density and position of the alkoxy chains around the molecular core.

Full text of DOI:10.1039/c5ra06620d

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Tuning the thermotropic properties of liquid
crystalline p-substituted aroylhydrazones†
Cite this: RSC Adv., 2015, 5, 44274
Hemant Kumar Singh,a Sachin Kumar Singh,a Rajib Nandi,b Madan Kumar Singh,a
Vijay Kumar,a Ranjan K. Singh,b D. S. Shankar Rao,c S. Krishna Prasadc
a
*
and Bachcha Singh
The synthesis and mesomorphic properties of forty substituted aroylhydrazones with peripheral mono-, di-
and tri- alkoxy chains derived from a p-amino aroylhydrazone core are described. The compounds with two
side chains exhibited a smectic A phase, while the compounds with six soft alkoxy side chains at symmetrical
positions formed a rectangular columnar mesophase. The structures of these mesophases were confirmed
by differential scanning calorimetry (DSC) analysis, polarized optical microscopy (POM) and powder X-ray
diffraction (XRD) studies. Raman studies with the help of density functional theory on some of the
mesogenic members have been performed to understand the changes in the intermolecular interactions
during phase transitions. A structure–property relationship has been deduced, and mesogenic properties
are found to be dependent on the chain length, density and position of the alkoxy chains around the
molecular core.
Received 13th April 2015
Accepted 8th May 2015
DOI: 10.1039/c5ra06620d
www.rsc.org/advances
azomethine moiety.18,19 Lai et al. synthesized a series of poly-
catenar aroylhydrazinato-nickel(II) metallo-mesogens showing
1. Introduction
columnar mesophases (Fig. 1B). These derivatives showed
interesting mesophase crossover phenomenon from rectan-
gular to hexagonal columnar phase with increasing alkoxy
chain length.20 Tschierske and Yelamaggad have reported
interesting room temperature mesophase of aroylhydrazones
(Fig. 1C). They combined 3,4,5- and 2,3,4-trialkoxy substitution
patterns on benzoyl- and benzylidene units respectively, to
obtain low melting columnar LC materials. The mesophase of
these derivatives were found due to adaptation of unusual
supramolecular helical organization of molecules by intermo-
lecular hydrogen bonding.21 Recently, our group has reported
calamitic mono- and disubstituted aroylhydrazone derivatives
showing variety of mesophases depends on their terminal
substitution patterns (Fig. 1D).22–25
In this work, we synthesized rigid, extended, mono- to
tricatenar alkoxy systems derived from aroylhydrazones. The
aroylhydrazone unit was extended in the p-benzoyl-position
using imine linking group. The mesophase behavior of
these compounds was investigated as a function of chain
length, density and position of alkoxy tails. Mesophase
Aroylhydrazones, hydrazine derivatives and their metal
complexes are some of the most versatile compounds that
exhibit a broad spectrum of biological, bactericidal and fungi-
cidal activities and are of great interest due to their analytical,
industrial and pharmacological importance.1–7 These
compounds can also manifest a wide spectrum of functional
properties such as redox activities, magnetism, luminescence,
supramolecular order, sensing probes, etc.8–11 Several synthetic
methodologies have been developed in the past to functionalize
the aroylhydrazone core at different ring positions.12–17 The
aroylhydrazone core (–C6H5–C(]O)–NH–N]CH–C6H5–) has,
benzoyl (–C6H5C]O–) and benzylidene (]CH–C6H5–) termi-
nals for easy incorporation of various suitable substituent and
derivatives. By proper design of the aroylhydrazone derivatives,
it is possible to obtain different types of liquid crystals (LCs) and
tune their mesomorphic potential, although examples of
mesogenic aroylhydrazones are very few. It was rstly explored
by McCabe et al. by design and synthesis of a series of nickel(II)
and copper(II) complexes of aroylhydrazone derivatives (Fig. 1A).
The mesomorphic nature of these complexes was found to be
strongly dependent on the nature of the substituent at the
crossover from typical smectic
A (SmA) to rectangular
columnar (Colr) mesophase was found in these derivatives
and investigated in detail by polarising optical microscopy
(POM), differential scanning calorimetry (DSC) and powder
X-ray diffraction (XRD) studies. Also the nature of inter-amide
hydrogen bonding (–C]O/H–N–) during phase transitions
(crystal / mesophase) was investigated by Raman spectro-
scopic studies.
aDepartment of Chemistry (Centre of Advance Study), Faculty of Science, Banaras
Hindu University, Varanasi-221005, India. E-mail: bsinghbhu@rediffmail.com
bDepartment of Physics (Centre of Advance Study), Faculty of Science, Banaras Hindu
University, Varanasi-221005, India
cCentre for Nano and So Matter Sciences, Jalahalli, Bangalore-560013, India
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c5ra06620d
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Fig. 1 (A) Mesogenic mono-alkoxy aroylhydrazone-nickel(II) complex reported by McCabe et al.18,19 (B) Polycatenar aroylhydrazone-nickel(II)
complexes reported by Lai et al.20 (C) Structure of non-symmetrical polycatenar aroylhydrazones reported by Yelamaggad et al.21 (D) Substituted
aroylhydrazones at benzylidene-22 and benzoyl- position23 reported by Singh et al.
2.2 Mesomorphic behaviour of novel substituted
2. Results and discussion
aroylhydrazone compounds
2.1 Synthesis
The thermotropic behaviour of the title aroylhydrazones were
The synthetic route for preparation of aroylhydrazone based
studied by combining thermo gravimetric analyses (TGA), DSC,
ligands is outlined in Scheme 1. Alkylation of 4-hydroxy-
POM and XRD studies (in selected cases). Transition tempera-
benzaldehyde with 1-bromoalkane in 2-butanone using potas-
sium carbonate leads to formation of 4-alkoxybenzaldehyde.
tures and their associated enthalpy, entropy changes are gath-
ered in Tables 1–3. The mesomorphic properties of these
Reaction of ethyl-4-aminobenzoate with hydrazine hydrate in
compounds are described accordingly two, four and six
re-uxing absolute ethanol gave 4-aminobenzohydrazide as
terminal chains (n ¼ 5–16) in the following sections.
white solid. The Schiff bases were obtained by the condensation
2.2.1 Compounds with two terminal chains. TGA
reaction of 4-aminobenzohydrazide with appropriate aldehydes
measurements performed on these compounds proved good
in reuxing ethanol. All the ligands were characterized by
elemental analyses and standard spectroscopic techniques. The
experimental procedures, synthesis of the intermediates and
analytical data are described in the ESI.†
ꢀ
thermal stability up to 250 C. DSC analysis showed that these
compounds exhibit several reversible transitions on the second
heating and cooling curve, indicating polymorphic nature of
compound (Fig. 2a and b). Such polymorphism has oen been
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Scheme 1 Reactions and reagents: (a) NH2NH2 (1.5 equiv.), refluxing in absolute EtOH, 12 h, 85–90%. (b) RBr (n equiv.), K2CO3 (4 ꢁ n equiv.), KI
(catalyst), refluxing in 2-butanone, 24–72 h, 70–85%. (c) Acetic acid (cat.), refluxing in EtOH, 12 h, 74–87%.
observed in Schiff base containing compounds.26 NMR experi- mesophase with similar pattern; that is, the mesomorphism is
ments also performed aer the DSC measurements and enantiotropic (Fig. 3).
revealed that the compounds did not degrade aer several
temperature cycles up to 250 C.
The smectic A mesophase behaviour was obtained for the
series of compounds 1 with lower and higher alkoxy chain
ꢀ
In the series of mesogens, 1 (n ¼ 5–8, 10, 12, 14, 16) with the length homologous derivatives (n ¼ 5–8, 10, 14, 16) with
moderate alkyl chain length (n ¼ 12) at benzylidene moiety continuous lowering in melting and clearing temperatures
shows ve endo- and three exothermic peaks in DSC thermo- without considerable changes in mesophase temperature
gram (Fig. 2a). POM observations reveal that upon heating from range. The mesophase temperature of the compounds ranged
crystal state to 171.6 ꢀC, focal conic texture corresponding to 204.8–231.5 ꢀC and 230.5–200.3 ꢀC in heating and cooling
SmA mesophase emerges, which further transforms to isotropic cycles, respectively. Table 1 summarizes the thermodynamic
liquid at 221.8 ꢀC. In cooling cycle, POM reveals the same parameters associated with the mesomorphic transitions of all
ꢀ
textural observations, which emerges from 219.4 C and solid- the alkoxy benzylidene derivatives.
ies at 162.2 ꢀC. Reheating regenerates the focal conic SmA
Table 1 Thermal transitions and corresponding thermodynamic parametersa
Compound
1 (n ¼ 5)
1 (n ¼ 6)
1 (n ¼ 7)
1 (n ¼ 8)
1 (n ¼ 10)
1 (n ¼ 12)
1 (n ¼ 14)
1 (n ¼ 16)
Heating T, ꢀC [DH, kJ molꢂ1; DS, J (molꢂ1 Kꢂ1)]
Cooling T, ꢀC [DH, kJ molꢂ1; DS, J (molꢂ1 Kꢂ1)]
Cr 96.5 (6.8; 18.4) Cr0 211.1 (45.5; 94.0) SmA 231.6 (5.5; 10.9) i
Cr 140.4 (14.6; 35.4) Cr0 195.1 (21.8; 46.7) SmA 230.2 (4.1; 8.1) i
Cr 111.4 (8.2; 21.3) Cr0 197.6 (38.4; 81.7) SmA 228.3 (6.1; 12.1) i
Cr 130.7 (11.3; 8.0) Cr0 187.4 (43.5; 98.7) SmA 226.9 (17.2; 34.4) i
Cr 121.5 (5.3; 14.0) Cr0 175.3 (40.7; 90.9) SmA 225.5 (16.2; 32.5) i
Cr 132.7 (70.9; 174.8) Cr0 171.6 (49.8; 111.9) SmA 221.9 (22.0; 44.7) i
Cr 121.6 (40.2; 101.9) Cr0 163.4 (27.4; 62.7) SmA 207.7 (6.9; 14.4) i
Cr 136.6 (3.4; 8.2) Cr0 162.3 (32.5; 74.6) SmA 204.8 (8.8; 18.5) i
i 230.5 (ꢂ5.2; ꢂ10.3) SmA 196.6 (ꢂ23.9; ꢂ50.9)
Cr0 191.6 (ꢂ8.7; ꢂ18.6) Cr
i 227.7 (ꢂ11.6; ꢂ23.2) SmA 187.6 (ꢂ18.6; ꢂ40.3)
Cr0 175.6 (ꢂ21.5; ꢂ47.8) Cr
i 223.9 (ꢂ6.0; ꢂ12.0) SmA 185.8 (ꢂ27.0; ꢂ58.7)
Cr0 153.8 (ꢂ6.0; ꢂ14.0) Cr
i 221.1 (ꢂ8.6; ꢂ17.4) SmA 170.6 (ꢂ30.9; ꢂ71.2)
Cr0 121.5 (ꢂ6.2; ꢂ15.6) Cr
i 221.9 (ꢂ10.4; ꢂ21.0) SmA 168.2 (ꢂ27.8; ꢂ63.0)
Cr0 136.3 (ꢂ9.0; ꢂ22.8) Cr
i 219.5 (ꢂ18.7; ꢂ38.0) SmA 162.3 (ꢂ40.3; ꢂ92.4)
Cr0 128.8 (ꢂ8.2; ꢂ20.3) Cr
i 202.9 (ꢂ4.2; ꢂ8.9) SmA 148.9 (ꢂ7.5; ꢂ17.8)
Cr0 122.4 (ꢂ5.4; 13.7) Cr
i 200.4 (ꢂ5.3; ꢂ11.1) SmA 152.1 (ꢂ22.0; ꢂ51.8)
Cr0 132.1 (8.5; 21.0) Cr
a
Abbreviations: Cr & Cr0 ¼ crystalline state, SmA ¼ smectic A mesophase, i ¼ isotropic liquid.
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Fig. 2 DSC thermograms of the compound 1 (a) n ¼ 12 and (b) n ¼ 14 showing enantiotropic mesophase
Fig. 3 Microphotographs of the compound 1 (n ¼ 12) in SmA phase in cooling cycle (a) broken focal conic texture of compound at 192.1 ꢀC, (b)
broken focal conic texture at 184.1 ꢀC and (c) SmA to crystal transition of the compound at 162.2 ꢀC.
XRD measurements were carried out on a representative temperature of 200 ꢀC is shown in Fig. 4a. The prole exhibits a
compound of the series, viz., 1 (n ¼ 12) exhibiting a wide range sharp intense low angle peak and a weak broad diffuse peak at
of the mesophase. The raw diffraction prole obtained at a wide angles, which are characteristic features of a layered
Fig. 4 X-ray measurements on the 1 (n ¼ 12) compound. (a) Raw XRD profile collected at 200 ꢀC, exhibiting a sharp low angle peak and a wide
angle diffuse maximum. (b) Thermal variation of the layer thickness.
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phase. The absence of any higher harmonic peaks corre- 1 (n ¼ 12) have been recorded to verify the presence of inter-
sponding to the low angle peak indicates the layered structure molecular hydrogen bonding in these systems (Fig. SI 11 and
to be of the classical type with a pure sinusoidal density 12†). The temperature dependent variation of C]O stretching
modulation. These features conrm the mesophase to be SmA and N–H stretching Raman bands is shown in Fig. 5. At room
in agreement with the POM observations. The thermal variation temperature C]O stretching and N–H stretching vibrations at
of the layer thickness (d) determined from tting the low angle ꢃ1652 and ꢃ3286 cmꢂ1 respectively conrm the intermolecular
peak to a Lorentzian aer a proper background treatment, is hydrogen bonding between the amide groups.21,27–29 In Cr–Cr0
shown in Fig. 4b. The negative thermal expansion of the layer transition, both bands shi lower indicating stronger hydrogen
thickness is not uncommon in the SmA phase. This is caused by bond network. In SmA phase, these bands become broad and
the fact that the alkyl chains stretch as the temperature is shied higher to 1675 cmꢂ1 and 3360 cmꢂ1 respectively. This
lowered. The rate of the expansion calculated by the slope d/dT indicates the breaking of hydrogen bonds associated with
(d) is ꢂ4.1 ꢁ 10ꢂ4 nm K which is typical of monomeric amide group during crystal to mesophase transition facilitating
compounds.
monomer formation in SmA phase. The calculated length of the
˚
The intermolecular hydrogen bond of –C]O/H–N- type has optimized structure of monomer (L) is ꢃ49.1 A (Fig. SI 13†)
been reported in the compounds containing amide linking whereas the interlayer distance d calculated from XRD in SmA
˚
group particularly in aryolhydrazones that are responsible for phase is ꢃ37.6 A. In case of L > d, the molecular unit in layer is
specic supramolecular order of mesogens and also help in monomeric and intercalation of the alkyl chains of the molecule
mesophase formation.21,24,27,28 In the view of above fact, between the layers exists as shown in Fig. 6.
temperature dependent Raman spectra of one of the compound
2.2.2 Compounds with four terminal chains. The
compounds 2 (n ¼ 5–8, 10, 12, 14, 16) and 3 (n ¼ 5–8, 10, 12, 14,
16) with four terminal chains at asymmetrical and symmetrical
positions (3,4 and 3,5 dialkoxy derivatives) were also prepared to
study the effect of side chain density on the formation of mes-
ophases. DSC analysis showed that these compounds with four
terminal chains exhibited one single reversible transition in
cooling and heating cycles. This single transit in DSC thermo-
grams is assigned to direct melting into isotropic liquid by POM
studies. Poor space lling by the four terminal chains for the
formation of columnar mesophase is attributed to the non-
mesomorphic behaviour of this series of compounds (Table SI
1 and 2†).
XRD patterns obtained for the compounds 2 and 3 (Fig. SI
14†) at temperatures below the isotropic phase displayed
several sharp peaks over the whole 2q (1ꢀ # 2q # 30ꢀ) angular
range and conrmed non-mesomorphic character of the
material. Interestingly, the lowest angle peak is far more intense
than other peaks suggesting that the solid phase may still have a
layered ordering with the terminal chains having substantial
gauche conformations.
Fig. 5 Peak position variation with temperature of C]O and N–H
stretching Raman bands of compound 1 (n ¼ 12).
2.2.3 Compounds with six terminal chains. Two classes of
compounds with unsymmetrical (2,3,4 trialkoxy) and symmet-
rical (3,4,5 trialkoxy) carbon chain density (4 and 5, n ¼ 5–8, 10,
12, 14, 16) were prepared under this category similar to the
compounds with four terminal chains described in the above
section in order to verify the role of alkoxy chain density as well
as position of terminal chains around the core group for
manifestation of mesogenicity in such derivatives. From TGA
analysis, the degradation temperature of the compounds 4 and
ꢀ
5 were found to be above 250 C.
The compounds of the series with unsymmetrical alkoxy
chains 4 (n ¼ 5–8, 10, 12, 14, 16) are non mesomorphic and
show sharp melting behaviour under POM and DSC studies.
XRD patterns obtained for the compounds at temperatures
below the isotropic phase displayed several sharp peaks
conrmed non-mesomorphic character of the material. The
melting point of all the compounds of the series are ranged
Fig. 6 Schematic representation of molecules in SmA phase.
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Table 2 Thermal transitions and corresponding thermodynamic parametersa
Compound
Heating T, ꢀC [DH, kJ molꢂ1; DS, J (molꢂ1 Kꢂ1)]
Cooling T, ꢀC [DH, kJ molꢂ1; DS, J (molꢂ1 Kꢂ1)]
4 (n ¼ 5)
4 (n ¼ 6)
4 (n ¼ 7)
4 (n ¼ 8)
4 (n ¼ 10)
4 (n ¼ 12)
4 (n ¼ 14)
4 (n ¼ 16)
Cr 78.3 (26.3; 74.7) Cr0 112.4 (76.3; 197.9) i
Cr 85.9 (15.1; 42.2) Cr0 103.9 (42.6; 113.0) i
Cr 102.1 (48.3; 128.8) i
Cr 94.7 (79.2; 215.3) i
Cr 82.7 (50.6; 192.9) i
i 104.6 (ꢂ41.9; ꢂ110.9) Cr
i 99.8 (ꢂ36.4; ꢂ97.6) Cr
i 95.9 (ꢂ72.9; ꢂ197.5) Cr
i 82.9 (ꢂ67.7; ꢂ190.0) Cr
i 72.9 (ꢂ60.8; ꢂ175.6) Cr
Cr 78.4 (58.4; 166.0) i
i 76.2 (ꢂ63.7; ꢂ182.4) Cr0 54.4 (ꢂ33.2; ꢂ101.3) Cr
i 68.5 (ꢂ30.3; ꢂ88.7) Cr
Cr 74.3 (64.1; 184.6) i
Cr 58.4 (57.2; 172.5) Cr0 72.2 (71.4; 206.7) i
i 70.43 (ꢂ39.7; ꢂ115.6) Cr0 48.6 (ꢂ22.1; ꢂ68.8) Cr
a
Abbreviations: Cr & Cr0 ¼ crystalline state, SmA ¼ smectic A mesophase, Colr ¼ rectangular columnar mesophase, i ¼ isotropic liquid.
Table 3 Thermal transitions and corresponding thermodynamic parametersa
Compound
Heating T, ꢀC [DH, kJ molꢂ1; DS, J (molꢂ1 Kꢂ1)]
Cooling T, ꢀC [DH, kJ molꢂ1; DS, J (molꢂ1 Kꢂ1)]
5 (n ¼ 5)
5 (n ¼ 6)
5 (n ¼ 7)
5 (n ¼ 8)
5 (n ¼ 10)
5 (n ¼ 12)
5 (n ¼ 14)
5 (n ¼ 16)
Cr 124.2 (18.2; 45.7) i
Cr 123.7 (24.5; 61.8) i
Cr 120.2 (21.7; 55.1) i
Cr 113.9 (31.1; 80.3) Colr 118.2 (4.0; 10.1) i
Cr 107.9 (28.9; 75.8) Colr 114.0 (2.0; 5.3) i
Cr 105.9 (35.5; 93.7) Colr 113.3 (8.4; 21.7) i
Cr 96.1 (34.7; 94.0) Colr 110.7 (7.2; 18.7) i
Cr 99.0 (40.3; 108.3) Colr 109.2 (7.3; 19.2) i
i 120.0 (ꢂ14.0; ꢂ35.6) Cr
i 119.9 (ꢂ26.2; ꢂ66.6) Cr
i 117.4 (ꢂ9.8; ꢂ25.1) Cr
i 116.4 (ꢂ4.0; ꢂ10.3) Colr 108.7 (ꢂ27.6; ꢂ72.2) Cr
i 111.4 (ꢂ2.1; ꢂ5.4) Colr 100.0 (ꢂ25.6; ꢂ68.6) Cr
i 111.0 (ꢂ8.3; ꢂ21.5) Colr 98.8 (ꢂ30.5; ꢂ82.0) Cr
i 106.3 (ꢂ7.0; ꢂ18.4) Colr 91.6 (ꢂ36.2; ꢂ99.2) Cr
i 105.8 (ꢂ6.6; ꢂ17.3) Colr 92.6 (ꢂ32.1; ꢂ87.8) Cr
a
Abbreviations: Cr ¼ crystalline state, Colr ¼ rectangular columnar mesophase, i ¼ isotropic liquid.
between 112.4–72.2 ꢀC and 104.6–70.4 ꢀC in heating and cooling
cycles respectively as shown in Table 2.
The compounds of the series with symmetrical alkoxy
chains 5(n ¼ 5–8, 10, 12, 14, 16), all exhibited the liquid crys-
talline behavior of columnar discotics except for short alkyl
chain lengths (n ¼ 5, 6 and 7) and were characterized by
DSC analysis, POM and XRD studies (for n ¼ 10). The phase
transition temperatures and enthalpies of compounds 5 are
given in Table 3.
The compounds with octyloxy to hexadecyloxy (n ¼ 8–16)
carbon chain length exhibited enantiotropic columnar meso-
phase. On heating the crystals transform substantially to
ꢀ
columnar mesophase above 99.0–113.9 C, whereas the tran-
sition of mesophases at ca. 116.3–105.8 ꢀC took place on
cooling from the isotropic phase for these compounds (Fig. 7).
The columnar rectangular phases of all compounds were
easily identied by polarizing optical microscopy (Fig. 8). The
compound with decyloxy carbon chain length (n ¼ 10) was also
Fig. 7 DSC thermogram of the compound 5 (n ¼ 10) showing
enantiotropic mesophase.
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Fig. 8 Microphotographs of the compound 5 (n ¼ 10) Colr phase in cooling cycle (a) at 109.1 ꢀC (b) at 104.2 ꢀC (c) 90.2 ꢀC.
studied by XRD to examine the mesophase structure. Fig. 9 a molten state. This columnar rectangular (Colr) mesophase
ꢀ
presents the diffraction prole obtained at T ¼ 100 C exhib- has p2mm plane group symmetry as calculated Miller indices
iting multiple sharp peaks at low angles and a broad diffuse of the observed peaks are such that, h + k is odd as well as
peak at wide angles, clearly points to a columnar phase. The even.30 Such symmetry of rectangular lattice for polycatenar
low angle peaks were then indexed; the four reection indices molecules has been observed rarely,31 only few examples to our
conrm very well to a rectangular lattice with the (hk) values knowledge been reported.28,32–34 The number of molecules
being (10), (01), (11) and (20); a ¼ 3.08 and b ¼ 2.19 nm as forming a columnar unit was found to be as one molecule per
lattice parameters. The diffuse and broad-scattering halo at columnar unit taking density of the organic molecule as 1 g
wide angle around d ¼ 0.44 nm is due to mainly liquid like cmꢂ3 and core–core stacking distance as 4.4 A. According to
˚
stacking of the cores along the column with aliphatic chains in p2mm symmetry requirements, one molecule is placed at the
corner of the columnar unit and these units are stacked to
columns, which are organized in a columnar rectangular
mesophase. The optimized diameters of disc shape molecule
˚
˚
estimated to be around 44.3 A and 29.4 A (Fig. SI 15†), indicate
that the columns are partial intercalation in the 2D rectan-
gular plane. The N–H stretching Raman band of 5 (n ¼ 10)
appears at 3340 cmꢂ1, that indicates absence of hydrogen
bonding between amides along the column in crystal as well as
in columnar phase (Fig. SI 16†). The schematic representation
of rectangular arrangement of compound 5 (n ¼ 10) in
columnar phase is shown in Fig. 10.
The homologous series of the compounds
4 with
unsymmetrical arrangements i.e. 2,3,4 trialkoxy derivatives
have lower melting (isotropic) temperature to that it's
symmetrical derivatives, 5. The non mesogenicity of such
derivatives may be due to inability of molecule to stack in
columns due to asymmetric arrangement of alkoxy termi-
nals. Also, absence of intermolecular hydrogen bonding
between layers rules out hexagonal chiral arrangement of
molecules as found in earlier similar report on polycatenar
derivatives of aroylhydrazone.21
Fig. 9 XRD pattern of the compound 5 (n ¼ 10) at 100 ꢀC.
Conclusions
We have synthesized lamellar and columnar liquid crystals by
substituting peripheral alkoxy benzylidene units at aroylhy-
drazone core. The mesomorphic behaviors of these compounds
were analyzed using various suitable techniques. The
compounds with one side chain (n ¼ 5–16) at both periphery
were found to be mesomorphic in nature, showing SmA meso-
phase. Temperature dependent XRD, Raman and DFT
Fig. 10 Schematic representation of columns in which molecules of
compound 5 (n ¼ 10) self-assemble in a rectangular arrangement.
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calculation revealed that these molecules were monomeric in 13 C. C. Paraschivescu, M. Matache, C. Dobrota, A. Nicolescu,
nature with intercalation of alkoxy chains in the SmA meso-
C. Maxim, C. Deleanu, I. C. Farcasanu and N. D. Hadade,
phase. The compounds with a total of six side chains (n ¼ 8–16)
J. Org. Chem., 2013, 78(6), 2670.
at symmetrical position exhibited columnar rectangular meso- 14 C. P. Hadjiantoniou-Maroulis, A. J. Maroulis, A. Terzis and
phase with p2mm plane group symmetry. However, the
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Acknowledgements
HKS (Senior Research Fellow) is grateful to the Council of
Scientic and Industrial Research (CSIR), New Delhi, India, for
nancial support. BS is grateful to DRDO, India (Project no.
ERIP/ER/1203053/M/01/1542) and DST, India (Project no. SR/S1/
IC-08/2012) for providing nancial assistance. RKS is grateful to
the DST, India for giving DST-FIST programme under which
Raman set-up was procured.
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