Mesophase behavior of new linear supramolecular hydrogen-bonding complexes

Article abstract of DOI:10.1039/c8ra07692h

Thermal and mesophase behavior of four new series of hydrogen-bonded supramolecular complexes (In/IIm) were investigated by differential scanning calorimetry and phases identified by polarized light microscopy. All hydrogen-bonded complexes formed from 4-

Full text of DOI:10.1039/c8ra07692h

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Mesophase behavior of new linear supramolecular
hydrogen-bonding complexes†
ab
Cite this: RSC Adv., 2018, 8, 34937
M. Hagarac and A. Aljuhanid
*
H. A. Ahmed,
Thermal and mesophase behavior of four new series of hydrogen-bonded supramolecular complexes (In/
IIm) were investigated by differential scanning calorimetry and phases identified by polarized light
microscopy. All hydrogen-bonded complexes formed from 4-alkoxyphenylazobenzoic acid (In) and 4-
(40-pyridylazophenyl)-400-alkoxybenzoates (IIm). The results revealed that the prepared complexes are
dimorphic, possessing smectic C and nematic phases. The comparison, made between the present
series and previously investigated simpler, In/IIIm and angular, In/IVm analogues, revealed that increasing
the length of the mesogenic core and/or linearity of complex increase the stabilities of both the smectic
C and nematic phases.
Received 15th September 2018
Accepted 4th October 2018
DOI: 10.1039/c8ra07692h
rsc.li/rsc-advances
pyridines and benzoic acids moieties was used to induce
nematic, smectic and columnar mesophases.5,37,38 On the
1. Introduction
other hand, the azobenzene units are of special interest due
to their ability for trans-cis-isomerization upon irradiation
with UV light. In supramolecular azo-based liquid crystals,
via hydrogen bonding interaction, the rigid-rod core is
lengthened, and thus induces liquid crystalline behaviour
that may not occur in the individual components.39,40 Such
induced mesomorphic behaviour is attributed to the forma-
tion of the elongated hydrogen-bonded complex. Moreover,
the induction of liquid crystalline character is also associated
with the strength of hydrogen bonds formed between the
interacting components. This would accordingly be affected
by the change in polarity and/or polarisability of both
components.
Mesomorphic properties of liquid crystal materials are
largely affected by any change in their molecular structure.
Several methods were reported to obtain highly stable nano
structured systems from anisotropic particles and liquid
crystals such as stable colloidal dispersions of halloysite clay
nanotubes.1–3 Hydrogen bonding between carboxyl and pyr-
idyl moieties proved to be extremely fruitful for the formation
of supramolecular hydrogen-bonded liquid crystals
(SMHBLCs).4–7 Thus, intermolecular hydrogen-bond interac-
tions have shown great potential in the preparation of new
liquid crystalline systems, especially in thermotropic liquid
crystals.8–12 Extensive researches have been focused on the
eld of hydrogen-bonded liquid crystalline complexes.13–18
Most of the SMHLCs studied are based on the rod-like
intermolecular hydrogen-bonding19–25 and there is much
interest towards the formation of angular supramolecular
hydrogen bonded liquid crystals.15 The concept of SMHLCs
has been successively applied in many applications in
scientic and technological elds.26–30 Number of hydrogen-
bonded binary systems, based on pyridine as proton accep-
tors and carboxylic acid derivatives as the proton donors,
have been investigated and reviewed and reviewed exten-
sively.5,31–36 More recently, hydrogen-bonding between
Continuing our work, the present study is to investigate
the thermal behavior resulting from intermolecular
hydrogen-bond
formation
between
the
4-alkox-
yphenylazobenzoic acids,41,42 In, and 4-(40-pyridylazophenyl)
400-alkoxybenzoates,19 IIm. Therefore, we constructed all
possible 1 : 1 supramolecular complexes In/IIm with various
lengths of the terminal alkoxy chains in order to monitor the
effect of similar and/or different proportionating of alkoxy-
chain length on the mesophase formation, shown in
Scheme 1. Also investigated, the effect of introducing addi-
tional azobenzene unit to the linear supramolecular
complexes previously reported19 through hydrogen-bond
formation between 4-alkoxy benzoic acids (IIIn) as proton
donors and 4-(40-pyridylazophenyl)400-alkoxybenzoates (IIm)
as proton acceptors (IIIn/IIm). A comparison was made, also
between the present series (In/IIm) and previously investi-
gated angular isomer, In/IVm,15 to investigate the effect of the
linearity of the structure on the mesophase stability.
aCollege of Sciences, Chemistry Department, Taibah University, Yanbu, Saudi Arabia.
E-mail: hmahmoud@taibahu.edu.sa; ahoda@sci.cu.edu.eg; mohamedhaggar@gmail.
com
bFaculty of Science, Department of Chemistry, Cairo University, Cairo, Egypt
cFaculty of Science, Chemistry Department, Alexandria University, Alexandria, Egypt
dFaculty of Sciences, Chemistry Department, Taibah University, Al-Madinah al-
Munawwarah, Saudi Arabia. E-mail: ateyatallah@hotmail.com
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c8ra07692h
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Scheme 1 Preparation of 4-alkoxyphenylazobenzoic acids In.
Calorimetric measurements were carried out using a TA
Instruments Co. Q20 Differential Scanning Calorimeter (DSC;
USA). The DSC was calibrated using the melting temperature
and enthalpy of indium and lead. DSC investigation was carried
out for small samples (2–3 mg) placed in aluminum pans. All
measurements were achieved upon heating to stability
temperature anꢁd1cooling to room temperature with heating rate
2. Experimental
4-Hexyloxy benzoic acid, 4-octoyloxy benzoic acid, 4-decyloxy
benzoic acid and 4-dodecyloxy benzoic acid were obtained from
Merck (Germany). N,N0-dicyclohexylcarbodiimide (DCC) and 4-
dimethylaminopyridine (DMAP) were purchased from Aldrich
(Wisconsin, USA). All chemicals were used without further
purication. All the solvents used such as dichloromethane,
ethanol and methanol were of pure grade and purchased from
Aldrich (Wisconsin, USA).
of 10 ꢀC min
in inert atmosphere of nitrogen gas (30
ml minꢁ1) and all transition recorded from the second heating
scan.
Scheme 2 Preparation of 4-(40-pyridylazophenyl)-400-alkyloxybenzoates IIm.
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Scheme 3 Preparation of 1 : 1 supramolecular hydrogen-bonded complexes (In/IIm).
Transition temperatures for the individual components
and their 1 : 1 associated complexes (In/IIm), were deter-
mined by DSC, and the types of the mesophase identied by
a standard polarized light microscope (PLM, Wild, Germany)
attached with Mettler FP82HT hot stage. The temperature is
measured by thermocouple attached to the temperature
controller. Measurements were made twice and the results
2.2. Preparation of ethyl 4-n-alkoxyphenylazobenzoates
These were prepared by the method described previously.41
Ethyl 4-hydroxyphenylazobenzoate (0.001 mol) in ethanolic
KOH (0.02 mol, 20 ml) to which the appropriate amount of 1-
bromoalkane (0.0012 mol) was added drop-wise while stirring.
Stirring was continued at room temperature for two days. The
solid separated was ltered off, the solution evaporated and the
residue crystallized twice from ethanol. The products were TLC
pure and give transition temperatures as given in the
literature.41
ꢀ
have accuracy in transition temperature within ꢂ0.2 C.
2.1. Preparation of ethyl 4-hydroxyphenylazobenzoate
2.3. Preparation of 4-alkoxyphenylazobenzoic acids In
Ethyl 4-aminobenzoate (0.01 mol) was dissolved in concen-
ꢀ
trated hydrochloric acid and cooled in ice-salt bath to 0 C. To The esters (2) were hydrolyzed to the corresponding acids by
the resulting solution, a cold aqueous solution of sodium nitrite reuxing in aqueous ethanolic potassium hydroxide (0.02 mol,
(0.03 mol) was added drop-wise with stirring. During the addi- 20 ml) for 24 hours then acidied by dilute HCl to give the
tion, the temperature did not exceed 2 ꢀC. Aer complete corresponding acids. Again the products were crystallized twice
addition, the cold mixture was added drop-wise to an ice-cold from ethanol to give TLC pure solids that give transition
solution of phenol (0.01 mol) in sodium hydroxide (0.03 mol). temperatures agreeing with those reported in the literature
The mixture was further stirred at 0 ꢀC for one hour then (Scheme 2).41,43
acidied with dilute hydrochloric acid. The solid separated was
4-[2-[4-(Hexyloxy)phenyl]diazenyl]benzoic acid. Yield 85%,
ltered and crystallized twice from ethanol. The product was 1H NMR (300 MHz, CDCl3): d/ppm: d ¼ 8.13 (m, 2H, Ar–H), 7.92
ꢀ
TLC pure and gave melting point 163 C that agreed with that (m, 4H, Ar–H), 7.18 (m, 2H, Ar–H), 4.09 (t, J ¼ 7.7 Hz, 2H,
reported in the literature.41
OCH2 CH2), 1.98–1.74 (m, 2H, OCH2CH2 ), 1.40–1.31 (m, 6H,
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Fig. 1 FTIR spectrum of the 4-decyloxyphenylazobenzoic acid, I10.
CH2), 0.93 (t, J ¼ 7.1 Hz, 3H, CH3). Elemental analyses: found CH2Cl2 : THF); the mixture was stirred at room temperature for
(calc.): C, 69.65 (69.92); H, 6.60 (6.79); N, 8.83 (8.58).
48 h. The solid materials were ltered off and the solvent was
removed under vacuum. The obtained crude product was
puried by recrystallization from ethanol.
2.4. Preparation of 4-(40-pyridylazophenyl)400-alkyloxybenzoate IIm
4-(40-Pyridylazophenyl)-400-hexyloxybenzoate. Yield 77% 1H
NMR (CDCl3) d 8.81 (d, J ¼ 8.3, 2H, Ar–H), 8.17 (d, J ¼ 8.5, 2H,
Ar–H), 8.05 (d, J ¼ 8.4, 2H, Ar–H), 7.70 (d, J ¼ 8.5, 2H, Ar–H), 7.43
(d, J ¼ 8.5, 2H, Ar–H), 6.70 (d, J ¼ 8.5, 2H, Ar–H), 4.08 (t, J ¼
4-(40-Pyridylazo)phenol (0.30 g, 1.35 mmol) with hexylox-
ybenzoic acid (0.30 g, 1.35 mmol), DCC (0.28 g, 1.35 mmol), and
few crystals of 4-dimethylaminopyridine (DMAP) as a catalyst,
were dissolved in 20 ml 25% mixture of CH2Cl2 and THF(1 : 3
Fig. 2 FTIR spectrum of 4-(40-pyridylazophenyl)400-octyloxybenzoate, II8.
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Fig. 3 FTIR spectra of the 1 : 1 supramolecular complex I10/II8.
6.5 Hz, 2H, OCH2 CH2), 1.91–1.79 (m, 2H, OCH2CH2 ), 1.59–1.22 temperature (Scheme 3). For example to prepare the supramo-
(m, 6H, CH2), 0.91 (t, J ¼ 6.8 Hz, 3H, CH3). Elemental analyses: lecular complex I10/II8: 0.0382 mg of 4-decyloxyphenylazo-
found (calc.): C, 71.76 (71.44); H, 6.63 (6.25); N, 10.22 (10.41).
benzoic acid, I10 and 0.0431 mg of 4-(40-pyridylazophenyl)-400-
octyloxybenzoate II8 were mixed together using the method
described above.
All diagrams constructed by plotting transition tempera-
tures of the supramolecular hydrogen-bonded complex versus
alkoxy-chain length (n or m), the symbol “o” denotes crystal-
mesophase, "C" smectic C-to-nematic mesophase and “,”
nematic–isotropic transitions.
2.5. Preparation of supramolecular hydrogen-bonded
complexes, In/IIm
Supramolecular complexes (In/IIm), in the 1 : 1 molar ratios of
any two complementary components, were prepared by melting
the appropriate amounts of each component, stirring to give an
intimate blend and then, cooling with stirring to room
Table 1 Phase transition temperatures (ꢀC), enthalpy of transitions (kJ molꢁ1) and transition entropies (J molꢁ1 Kꢁ1), of the 1 : 1 supramolecular
complexes (In/IIm)a
System
TCr1–Cr2
TCr2–SmC
DHCr2–SmC
TSmC–N
DHSmC–N
DSSmC–N
TN–I
DHN–I
DSN–I
I6/II8
106.3
91.3
153.2
149.4
136.9
133.8
149.4
135.0
133.2
123.5
152.5
141.9
131.9
128.2
153.6
138.8
134.4
135
37.1
40.5
29.8
32.0
33.8
32.9
27.2
39.0
41.1
29.5
34.5
32.8
39.7
31.9
38.2
31.5
230.6
232.5
231.9
229.5
191.0
204.4
205.6
206.8
193.0
199.0
210.0
215.6
198.0
202.0
205.0
212.0
5.7
3.6
3.9
2.8
4.1
3.0
2.1
2.9
4.6
2.0
3.6
2.5
3.8
3.7
3.1
2.7
12.6
7.9
8.2
5.8
8.8
6.3
4.4
6.0
9.9
4.2
7.5
5.1
8.1
7.8
6.5
5.6
245.7
244.4
236.7
235.4
229.4
230.0
223.0
221.3
240.7
236.1
230.0
231.3
234.4
229.3
225.0
220.1
3.1
3.0
2.7
2.0
2.8
2.2
1.8
2.1
2.3
1.7
2.3
2.0
2.4
2.7
2.2
1.9
6.2
5.9
5.5
3.9
5.6
4.3
3.6
4.2
4.5
3.3
4.6
4.0
4.7
5.4
4.4
3.9
I6/II10
I6/II12
I6/II14
I8/II8
126.3
118.8
104.4
104.0
104.4
105.0
126.3
131.9
111.3
114.2
103.1
112.5
118.1
122.0
I8/II10
I8/II12
I8/II14
I10/II8
I10/II10
I10/II12
I10/II14
I12/II8
I12/II10
I12/II12
I12/II14
a
Abbreviations: TCr1–Cr2 ¼ crystal to crystal transition; TCr2–SmC ¼ crystal to smectic C phase transition; TSmC–N ¼ smectic C to nematic transition;
TN–I ¼ nematic to isotropic liquid transition. DHCr2–SmC ¼ crystal to smectic C phase transition; DHSmC–N ¼ smectic C to nematic transition; DHN–I
nematic to isotropic liquid transition; DSSmC–N ¼ smectic C to nematic transition; DSN–I ¼ nematic to isotropic liquid transition.
¼
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Fig. 4 Effect of the alkoxy-chain length (m) of the pyridine-based derivatives (IIm) on mesophase behavior of the 1 : 1 supramolecular hydrogen-
bonded complexes, (a) n ¼ 6; (b) n ¼ 8; (c) n ¼ 10: (d) n ¼ 12, TCr1–Cr2 ¼ crystal 1 to crystal 2 transition (B); TCr2–SmC ¼ crystal 2 to smectic C phase
transition (>); TSmC–N ¼ smectic C to nematic transition (C);TN–I ¼ nematic to isotropic liquid transition (,).
The infrared absorption spectra for all the homologues (In) were
found to be identical with the mesomeric shi of the carboxylic
carbonyl which attributed to the peak at 1678.5 cmꢁ1. There-
fore, the alkoxy-chain length (n) has no signicant effect on the
wave number of the peaks. This specic band shows that the
carboxylic acid exists in the dimer form shown in Scheme 3 via
intermolecular hydrogen bonding between the carboxylic
groups.19 Similarly, the spectral data of the proton acceptors,
IIm, shows that the alkyl chain length has again no effect on the
observed IR spectra for a given homologues series. In order to
conrm the formation of the supramolecular complexes, In/IIm,
IR spectra for the prepared complexes were measured. Fig. 3
shows the IR spectra of the complex I10/II8 prepared from equal
molar amounts of I10 and II8. A comparative IR spectra of I10,
II8, and I10/II8 is shown in Fig. 3. It had been reported that43–47
the carbonyl stretching region as well as the Fermi resonance
vibration bands (A-type, 3100 cmꢁ1; C-type, 1925 cmꢁ1) in the
spectra of the complex is an important evidence of intermo-
2.6. Structural conrmation
The purity of the prepared compounds were checked with thin-
layer chromatography using TLC-sheets coated with silica gel
(E. Merck), whereby single spots were detected by a UV-lamp.
The molecular formulae of the prepared compounds were
conrmed via elemental analyses, infrared, 1H-NMR, and
mass spectroscopy. The results agreed, within the permissible
limits, with the proposed structures and with those reported in
the literature.15,19
The formation of the supramolecular complexes (In/IIm)
were conrmed by DSC investigation as well as Fourier
Transform Infrared Spectroscopy (FTIR), which carried out
using Nicolet iS 10 Thermo scientic.
3. Results and discussion
3.1. Fourier transform infrared spectroscopy (FTIR)
Infrared spectra measurements were performed for the indi-
vidual components i. e. 4-alkoxyphenylazo benzoic acids (In)
and 4-(40-pyridylazophenyl)400-alkoxybenzoates (IIm) as well as
to their supramolecular complexes (In/IIm). For example, the IR
spectrum of I10 and II8 are given in Fig. 1 and 2, respectively.
lecular hydrogen bonding, where, the lower wave number (
¼
1678.5 cmꢁ1) of C]O group stretching vibration of the cyclic
carboxylic acid is shied to a higher wave number (
¼
1681.9 cmꢁ1) of the hydrogen-bonded dimers.
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Fig. 5 Effect of the alkoxy-chain length (n) of the pyridine-based derivatives (In) on mesophase behavior of the 1 : 1 supramolecular hydrogen-
bonded complexes, (a) m ¼ 8; (b) m ¼ 10; (c) m ¼ 12: (d) m ¼ 14, TCr1–Cr2 ¼ crystal 1 to crystal 2 transition (B); TCr2–SmC ¼ crystal 2 to smectic C
phase transition (>); TSmC–N ¼ smectic C to nematic transition (C);TN–I ¼ nematic to isotropic liquid transition (,).
the acid complement and another against (m) on the
pyridine-based complement in Fig. 4 and 5; respectively. As
can be seen from Table 1, Fig. 4 and 5, independent of either
n or m of the acid and base components, smectic C and
nematic mesophases are exhibited by all complexes in addi-
tion to, two crystalline phases given as Cr1 and Cr2. It can
also be seen from Fig. 4 that the nematic phase range
decreases gradually with the increase of the acid alkoxy-chain
length (n). SmC phase range is increasing with increasing the
acid alkoxy-chain length (n) and decreases gradually with the
increase of base alkoxy-chain length (m).
Fig. 4 showed that for a given value of m, the melting
temperatures of the supramolecular complexes are slightly
affected by the alkoxy-chain length of the acid complement (n).
Therefore, the acid In or the azo-pyridine IIm components
exhibit very small range of N phase, the resulted complexes In/
IIm constructed via intermolecular hydrogen bond showed an
nematic phase with relatively wide range. Representative
examples of polarizing optical microscopic images of the
mesophases are shown in Fig. 6. Fig. 6 show images of SmA
phase of azo-pyridine II8, SmC phase and schlieren texture of
nematic phase of the dimorphic complex I10/II8.
3.2. Phase behavior of 1 : 1 molar mixtures as a function of
the alkoxy-chain length
The phase behavior of the prepared complexes In/IIm was
investigated by PLM and DSC. PLM was used to detect phase
transition temperatures as well as textures of the liquid crystal
phases exhibited by the complexes In/IIm. PLM observations
were veried by the DSC measurements and types of meso-
phases were identied for all prepared supramolecular
complexes In/IIm.
It should be mentioned that, the mesophase behavior of
the prepared 4-alkoxy phenylazo-benzoic acids In exhibit
smectic C phase (SmC) with relatively high transition
temperatures and nematic phase with very small range,15,41
while the azopyridines IIm exhibit smectic A phase (SmA)
except the lower chain compound II8 is dimorphic possess-
ing SmA and nematic phases.19 Therefore, it was interesting
to investigate the phase behavior of the complexes resulting
from mixing compounds In and IIm.
Transition temperatures and their corresponding values
of transition enthalpies, as measured by DSC, for the 1 : 1
molar supramolecular complexes In/IIm are collected in
Table 1. All transition temperatures were represented
graphically once as a function of alkoxy-chain length (n) on
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Fig. 6 PLM textures of (a) SmA phase of II8 at 105.0 ꢀC; (b) SmC phase of complex I10/II8 at 183.0 ꢀC; and (c) nematic phase of the complex I10/
II8 at 225.0 ꢀC.
the previously investigated angular complexes (In/IVm) in which
only the base complement (IIm) is replaced by the 4-(30-pyr-
idylazophenyl)400-alkoxybenzoates, IVm.15 In such a comparison,
the effect of a modication will be investigated on the stability
of the mesophase (TC) as well as the type of mesophase
observed. Fig. 8 represents the TC dependencies on the alkoxy-
chain length (n) attached to the common 4-n-alkoxyphenylazo
benzoic acid complement (In) for these two, linear and angular,
complexes.
3.3. Effect of the extra phenylazo group on the mesophase
behaviour of the supramolecular hydrogen-bonded complexes
In order to investigate the effect of incorporating an extra
phenylazo group to molecules of the simple 4-alkoxybenzoic
acids (IIIn) on their mesophase behaviour of 1 : 1 molar
mixtures with the 4-(40-pyridylazophenyl)400-alkoxybenzoates
(IIIn/IIm), a comparison was made between the mesophase
stabilities (TC) of 4-n-alkoxyphenylazo benzoic acids (In) supra-
molecular hydrogen-bonded complexes (In/IIm) and their cor-
responding 4-n-alkoxy benzoic acids (IIIn/IIm),19 as a function of
alkoxy-chain length (n) and represented graphically in Fig. 7.
The study revealed that increasing the length of the mesogenic
core by a phenylazo moiety resulted in an increase of the
stability of both the smectic and nematic mesophases. In
addition, the SmC mesophase range observed in the present
investigated mixtures In/IIm has been increased upon incor-
poration of the phenylazo group in IIIn/IIm.
3.5. Entropy changes
The entropies of the smectic C–to-nematic and nematic-to–
isotropic transitions were estimated for all the 1 : 1 supramo-
lecular hydrogen-bonded complexes (In/IIm), and the results are
appended to Table 1. As seen from Table 1, independent of the
length of the alkoxy-chains (n or m), all entropies of N–I tran-
sitions (DSN–I) are of lower values than those of the corre-
sponding DSSmC–N transitions. The decrease observed in DSN–I
is presumably a reection of the increase in the biaxiality of the
mesogenic group, resulted in the exible terminal alkoxy-chain,
3.4. Comparison between isomeric linear and angular
supramolecular hydrogen-bonded complexes
It is interesting to compare the mesophase stability (TC) of the being less strongly anchored at its end, giving the resulting
present series of linear supramolecular complexes (In/IIm) with decrease in conformational entropy.40 This dependency
Fig. 7 Effect of alkoxy-chain length (m) on mesophase behavior of the In/IIm and IIIn/IIm 1 : 1 supramolecular complexes.
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Fig. 8 Effect of alkoxy-chain length (m) on mesophase behavior of the In/IIm and In/IVm supramolecular complexes.
indicates that the length of the terminal substituents, whether stabilities of both the smectic C and nematic mesophases. It
on the acid (n) or the base (m) complements, has led to an was also observed that the entropy change vary irregularly with
irregular DSN–I. An explanation that the entropies do not either of the alkoxy-chain length n or m.
correlate well with either of the two terminal alkoxy-chain
length (n or m), may be related to the irregular change of
lateral adhesion upon the increase of the total molecular
length.48
Conflicts of interest
The authors declare no conict of interest.
4. Conclusion
Acknowledgements
New types of 1 : 1 hydrogen-bonded supramolecular complexes
Authors gratefully acknowledge the Deanship of Scientic
were prepared. The formation of complexes via intermolecular
Research, Taibah University for the support of this research
hydrogen bond between the complementary components was
work, research group No. 60333.
conrmed by DSC and FTIR spectroscopy. It was found that,
their supramolecular complexes In/IIm exhibit relatively high
range nematic phase in addition to the SmC phase. Moreover,
the nematic phases are exhibited by all complexes regardless of
References
the length of the terminal alkoxy chains either on the proton
donor In or the proton acceptor IIm. A comparison was made
between the present series of complexes and the previously
investigated angular, In/IVm, and simple linear, IIIn/IIm,
analogues, revealed that increasing the length of the mesogenic
core, by inclusion of a phenylazo moiety, increases the
1 A. A. E. Sakr, T. Zaki, O. Elgabry, M. A. Ebiad, S. M. El-Sabagh
and M. M. Emara, Appl. Clay Sci., 2018, 160, 263–269.
2 S. Dutt, P. F. Siril and S. Remita, RSC Adv., 2017, 7, 5733–
5750.
3 L. Lisuzzo, G. Cavallaro, F. Parisi, S. Milioto and G. Lazzara,
Ceram. Int., 2018.
This journal is © The Royal Society of Chemistry 2018
RSC Adv., 2018, 8, 34937–34946 | 34945

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Paper
4 D. Demus, J. W. Goodby, G. W. Gray, H. W. Spiess and V. Vill, 26 R. Dong, Y. Zhou, X. Huang, X. Zhu, Y. Lu and J. Shen, Adv.
Low Molecular Weight Liquid Crystals I: Calamitic Liquid Mater., 2015, 27, 498–526.
Crystals, Handbook of Liquid Crystals, vol. 2A, John Wiley & 27 Y. Yang and M. W. Urban, Chem. Soc. Rev., 2013, 42, 7446–
Sons, 2011. 7467.
5 C. M. Paleos and D. Tsiourvas, Liq. Cryst., 2001, 28, 1127– 28 K. Liu, Y. Kang, Z. Wang and X. Zhang, Adv. Mater., 2013, 25,
1161. 5530–5548.
6 C. M. Paleos and D. Tsiourvas, Angew. Chem., Int. Ed. Engl., 29 X. Yan, F. Wang, B. Zheng and F. Huang, Chem. Soc. Rev.,
1995, 34, 1696–1711. 2012, 41, 6042–6065.
7 M. Naoum, A. Fahmi and M. Alaasar, Mol. Cryst. Liq. Cryst., 30 D. Gonzalez-Rodrıguez and A. P. Schenning, Chem. Mater.,
2008, 482, 57–70. 2010, 23, 310–325.
8 T. Kato and J. M. Frechet, J. Am. Chem. Soc., 1989, 111, 8533– 31 T. Kato, in Handbook of Liquid Crystals, ed. D. Demus, J. W.
´
´
8534.
Goodby, G. W. Gray, H.-W. Spiess and V. Vill, Wiley-VCH,
Weinheim, 1998, vol. 2B, pp. 969–979.
9 T. Kato and J. M. Frechet, Macromolecules, 1989, 22, 3818–
3819.
32 T. Kato, N. Mizoshita and K. Kanie, Macromol. Rapid
Commun., 2001, 22, 797–814.
33 T. Kato, Science, 2002, 295, 2414–2418.
10 A. J. Thote and R. B. Gupta, Ind. Eng. Chem. Res., 2003, 42,
1129–1136.
11 M.-J. Brienne, J. Gabard, J.-M. Lehn and I. Stibor, J. Chem. 34 C. Tschierske, J. Mater. Chem., 2001, 11, 2647–2671.
Soc., Chem. Commun., 1989, 1868–1870.
12 H. Ahmed, M. Hagar, M. Alaasar and M. Naoum, Liq. Cryst.,
2018, 1–10.
35 T. Kato, N. Mizoshita and K. Kishimoto, Angew. Chem., Int.
Ed., 2006, 45, 38–68.
36 J.-M. Lehn, Science, 1993, 260, 1762–1764.
13 J. W. Goodby, R. J. Mandle, E. J. Davis, T. Zhong and 37 A. Kohlmeier and D. Janietz, Liq. Cryst., 2007, 34, 65–71.
S. J. Cowling, Liq. Cryst., 2015, 42, 593–622. 38 T. Kato and Y. Kamikawa, Handbook of liquid crystals, 2014.
14 D. Janietz and M. Bauer, Macromol. Chem. Phys., 1991, 192, 39 S. M. Jansze, A. Martınez-Felipe, J. M. Storey, A. T. Marcelis
´
2635–2640.
and C. T. Imrie, Angew. Chem., 2015, 127, 653–656.
40 P. J. Collings, M. Hird and C. Tschierske, Angew. Chem., Int.
Ed. Engl., 1997, 36, 2017.
41 D. Janietz and M. Bauer, Macromol. Chem. Phys., 1991, 192,
2635–2640.
15 H. Ahmed and M. Naoum, Liq. Cryst., 2016, 43, 222–234.
16 M. Fouzai, R. Hamdi, S. Ghrab, T. Soltani, A. Ionescu and
T. Othman, J. Mol. Liq., 2018, 249, 1279–1286.
17 M. Alaasar, S. Poppe, Q. Dong, F. Liu and C. Tschierske,
Chem. Commun., 2016, 52, 13869–13872.
42 H. Ahmed, M. Naoum and G. Saad, Liq. Cryst., 2016, 43,
1259–1267.
18 H. K. Bisoyi and Q. Li, Chem. Rev., 2016, 116, 15089–15166.
19 M. Naoum, A. Fahmi and M. Alaasar, Mol. Cryst. Liq. Cryst., 43 M. Lizu, M. Lutfor, N. Surugau, S. How and S. E. Arshad, Mol.
2008, 487, 74–91. Cryst. Liq. Cryst., 2010, 528, 64–73.
20 M. Okumu¸s and ¸S. Ozgan, Liq. Cryst., 2014, 41, 1293–1302. 44 W. Cleland and M. M. Kreevoy, Science, 1994, 264, 1887–
¨
21 A. Ashok Kumar, B. Sridevi, M. Srinivasulu, P. Chalapathi
and D. Potukuchi, Liq. Cryst., 2014, 41, 184–196.
22 J. R. Wolf, T. Zhao, C. Landorf and D. J. Dyer, Liq. Cryst.,
2014, 41, 721–730.
1890.
45 A. Martinez-Felipe, A. G. Cook, J. P. Abberley, R. Walker,
J. M. Storey and C. T. Imrie, RSC Adv., 2016, 6, 108164–
108179.
´
23 S. Sreehari Sastry, K. Lakshmi Sarada, K. Mallika, 46 A. Martınez-Felipe and C. T. Imrie, J. Mol. Struct., 2015, 1100,
C. Nageswara Rao, S. Lakhminarayana and H. Sie Tiong,
429–437.
Liq. Cryst., 2014, 41, 1483–1494.
47 A. Ghanem and C. Noel, Mol. Cryst. Liq. Cryst., 1987, 150,
447–472.
´
24 M. D. Miranda, F. V. Chavez, T. M. Maria, M. E. S. Eusebio,
˜
P. Sebastiao and M. R. Silva, Liq. Cryst., 2014, 41, 1743–1751. 48 C. Imrie, Liq. Cryst., 1989, 6, 391–396.
´
25 D. A. Paterson, A. Martınez-Felipe, S. M. Jansze, A. TM
Marcelis, J. MD Storey and C. T. Imrie, Liq. Cryst., 2015, 42,
928–939.
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