Efficient and practical method for the synthesis of hydrophobic azines as liquid crystalline materials

Article abstract of DOI:10.1080/15421406.2017.1301872

A series of hydrophobic symmetrical azines: 1,2-bis[4-(n-alkoxy)benzylidene]hydrazine (where, n-alkoxy: O(CH₂)_nH, n = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 16, or 18) have been prepared following an efficient and practical method. These compounds have been synthesized via the condensation reaction of hydrazine hydrate and appropriately 4-(n-alkoxy) benzaldehydes in acidic medium under ambient conditions. The prepared organic compounds have been characterized and their structures were elucidated depending upon micro-elemental analysis and spectral data (IR, UV-Vis, ¹HNMR, ¹³C{¹H}NMR, 2D ¹H-¹H-cozy, 2D ¹H-¹³C-HSQC, and mass spectra). Liquid crystalline behavior of the prepared compounds was studied using polarized light optical microscopy and differential scanning calorimetry techniques. This study revealed that all the compounds displayed enantiotropic liquid crystal properties, exhibiting smectic and nematic mesophases.

Full text of DOI:10.1080/15421406.2017.1301872

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Efficient and practical method for the synthesis of
hydrophobic azines as liquid crystalline materials
Ali Jasim Hammood, Ahmed Fadhel H. Kased, Ahmed Jasim M. Al-Karawi,
Sameem R. Raseen, Ivan Hameed R. Tomi & Al-Ameen Bariz Omar Ali
To cite this article: Ali Jasim Hammood, Ahmed Fadhel H. Kased, Ahmed Jasim M. Al-Karawi,
Sameem R. Raseen, Ivan Hameed R. Tomi & Al-Ameen Bariz Omar Ali (2017) Efficient and
practical method for the synthesis of hydrophobic azines as liquid crystalline materials, Molecular
Crystals and Liquid Crystals, 648:1, 114-129, DOI: 10.1080/15421406.2017.1301872
To link to this article: http://dx.doi.org/10.1080/15421406.2017.1301872
Published online: 28 Jun 2017.
Submit your article to this journal
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
http://www.tandfonline.com/action/journalInformation?journalCode=gmcl20
Download by: [The UC San Diego Library]
Date: 29 June 2017, At: 02:38

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
https://doi.org/./..
Efficient and practical method for the synthesis of hydrophobic
azines as liquid crystalline materials
Ali Jasim Hammood, Ahmed Fadhel H. Kased, Ahmed Jasim M. Al-Karawi,
Sameem R. Raseen, Ivan Hameed R. Tomi, and Al-Ameen Bariz Omar Ali
Department of Chemistry, College of Science, Al-Mustansiriya University, Baghdad, Iraq
ABSTRACT
KEYWORDS
Hydrophobic symmetrical
azines; enantiotropic liquid
crystal; mesogenic
compounds
A
series of hydrophobic symmetrical azines: 1,2-bis[4-(n-alkoxy)
benzylidene]hydrazine (where, n-alkoxy: O(CH2)nH, n = 1, 2, 3, 4, 5,
6, 7, 8, 9, 10, 12, 16, or 18) have been prepared following an efficient
and practical method. These compounds have been synthesized via
the condensation reaction of hydrazine hydrate and appropriately
4-(n-alkoxy) benzaldehydes in acidic medium under ambient condi-
tions. The prepared organic compounds have been characterized and
their structures were elucidated depending upon micro-elemental
analysis and spectral data (IR, UV-Vis, 1HNMR, 13C{1H}NMR, 2D 1H-1H-cozy,
2D 1H-13C-HSQC, and mass spectra). Liquid crystalline behavior of
the prepared compounds was studied using polarized light optical
microscopy and differential scanning calorimetry techniques. This
study revealed that all the compounds displayed enantiotropic liquid
crystal properties, exhibiting smectic and nematic mesophases.
Introduction
Azines, N-N linked di-amines [1, 2], are extremely useful compounds, and recently they have
received attention because of their utility in a number of interesting reactions and applications,
specifically their biological properties [3, 4], the design of metal complexes [5, 6], potential
application in bond formation, nonlinear optical materials [7], and their uses in the purifi-
cation and characterization of carbonyl compounds [8]. Furthermore, azines are found to be
intermediates for the preparation of several pharmacological compounds [9].
Liquid crystal (LC) or polymorphism is an intermediate state of matter – in-between
liquid and crystals. It must possess some typical properties of a liquid (e.g., fluidity, inability
to support shear formation, and coalescence of droplets) as well as some crystalline prop-
erties (anisotropy in optical, electrical, and magnetic properties, periodic arrangement of
molecules in one spatial direction, etc.). Polymorphism can be classified in different ways.
Thermotropic polymorphism (representing the most common polymorphisms) means that
different polymorphs are obtained by the action of temperature (i.e., by heating or cooling).
In other cases, different crystal phases can be obtained by the action of solvents [10–12]. If the
transition from one form to another is reversible, the polymorphism is called enantiotropic;
CONTACT Ahmed Jasim M. Al-Karawi
Science,
ahmedalkarawi@uomustansiriyah.edu.iq
Department of Chemistry, College of
Al-Mustansiriya University, P.O. Box , Baghdad, Iraq.
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
115
if it is irreversible, the polymorphism is classified as monotropic. Thermotropic nematic LCs
represent the most technologically important LC compounds. It’s usually composed of rigid
rod-like or discal molecules [13], and widely used as operating fluid in LC displays (LCDs).
In 1959, a series of azine-type LCs were synthesized [14], which had high clearing points.
Since then, many experimental and theoretical studies [15–21] were made on the synthesis
of azine-type LCs using different synthetic approaches. In this work, we report the synthesis,
characterization, and mesomorphic properties of a series of hydrophobic azine derivatives:
1,2-bis[4-(n-alkoxy)benzylidene]hydrazine (where n-alkoxy: O(CH2)nH, n = 1, 2, 3, 4, 5, 6,
7, 8, 9, 10, 12, 16, or 18) compounds with a very simple, efficient, and convenient method.
Experimental
Physical measurements
Electronic spectra were measured in the region (200–800 nm) for (5×10−5 M) in
dichloromethane at (RT) by using a Varin Cary 100 Conc. spectrophotometer. Elemen-
tal analyses (C, H, and N) were carried out on a EuroEA 3000 Elemental Analyzer. Infrared
(IR) spectra were preformed in the region (4000–600 cm−1) using an 8400S-FTIR Shimadzu
1
1
1
spectrophotometer. HNMR, 13C{1H}NMR, 2D H-1H-cozy, and 2D H-13C-HSQC spec-
tra were recorded in CDCl3 using a Brucker 400-MHz spectrometer. Mass spectra were
obtained using a GC-DIMS QP 2010 Ultra spectrometer and Orbitrap LTQ XL-Thermo
Fisher scientific mass spectrometer. Differential scanning calorimetry (DSC) thermograms
were carried out in a nitrogen atmosphere at a heating and cooling rate of 5.0°C/min using
Linseis STA PT-1000 equipment, which was pre-calibrated. The equipment was provided
with an autocool system. Liquid crystalline mesophases of the compounds were obtained by
PW-BK5000R microscope equipped with HS-400 (KER3100-08S) heating stage.
Materials
All the reagents were available commercially (Germany) and were used without further
purification: 4-hydroxybenzaldehyde (98%, Fluka Co.), 1-iodomethane (98%, Aldrich Co.),
1-bromoethane (99%, Aldrich Co.), 1-bromopropane (99%, Aldrich Co.), 1-bromobutane
(98%, CDH Co.), 1-bromopentane (99%, Aldrich Co.), 1-bromohexane (98%, Aldrich Co.),
1-bromoheptane (99%, Aldrich Co.), 1-bromooctane (99%, Aldrich Co.), 1-bromononane
(99%, Aldrich Co.), 1-bromodecane (98%, Aldrich Co.), 1-bromododecane (97%, Aldrich
Co.), 1-bromohexadecane (97%, Aldrich Co.), 1-bromooctadecane (97%, Aldrich Co.),
potassium hydroxide (85%, SDFCL Co.), sodium sulfate anhydrous (99%, Aldrich Co.),
hydrazine hydrate (80%, Sigma-Aldrich Co.), and acetic acid (100%, Aldrich Co.). Solvents
used in the synthesis were distilled from appropriate drying agents immediately prior to use.
Preparation of 4-(n-alkoxy)benzaldehyde (general procedure) (A1–A13)
These compounds were prepared according to the Williamson synthesis of ethers by a known
method [22–24]. 4-hydroxybenzaldehyde (8.72 g, 71.5 mmol) was added to a solution of
potassium hydroxide (4 g) in ethanol (60 mL). The mixture was treated with n-alkyl halide
(71.5 mmol) (methyl iodide was used in the preparation of A1, while n-alkylbromide used in
the preparation of A1–A13) and heated under reflux. The reaction was monitored by thin-layer
chromatography (TLC) using chloroform as eluent, and the optimal time of each reaction was

116
A. J. HAMMOOD ET AL.
Table . Reaction conditions and quantities for the preparation of -(n-alkoxy)benzaldehyde compounds.
Compound
Alkylhalide weight (g)
Reaction time (h)
Rf
Yield (%)
A
.∗
.
.
.
.
.
.
.
.
.
.
.
.




.
.
.
.
.
.
.
.
.
.
.













A
A
A
A
A
A
A
A
A
A
A
A









.
.
∗Methyl iodide was used.
determined. The ethanol was evaporated and the residue was dissolved in diethyl ether. The
ethereal was washed with an aqueous solution of potassium hydroxide (10%) followed by
water until a pH = 7 was obtained. The organic layer was dried over sodium sulfate anhy-
drous and evaporated to give the desired product. The details of the reaction conditions for
the preparation of each compound are described in Table 1.
4-methoxybenzaldehyde (A1)
Yield = 65%. Characteristic spectroscopic data: FTIR (U/cm−1): 2970 (w, υas(C–H) of CH3
group), 2870 (w, υs(C–H) of CH3 group), 2922 (w, υas(C–H) of CH2 group), 2841 (w, υs(C–
H) of CH2 group), 3070 (w, υ(C–H) aromatic), 2740 (w-m, υ(C–H) aldehydic), 1680 (s,
υ(C=O)), 1599, 1575, and 1510 (s, m, m, υ(C=C) aromatic), 1255 (s, υ(C–O)), 1460 (m,
δ (C–H)).
4-ethoxybenzaldehyde (A2)
Yield = 70%. Characteristic spectroscopic data: FTIR (U/cm−1): 2981 (w, υas(C–H) of CH3
group), 2869 (w, υs(C–H) of CH3 group), 2933 (w-m, υas(C–H) of CH2 group), 2829 (w-m,
υs(C–H) of CH2 group), 3072 (w, υ(C–H) aromatic), 2729 (w-m, υ(C–H) aldehydic), 1681
(s, υ(C=O)), 1596, 1575 and 1508 (s, m, m, υ(C=C) aromatic), 1251 (s, υ(C–O)), 1475 (m,
δ(C–H)).
4-propyloxybenzaldehyde (A3)
Yield = 77%. Characteristic spectroscopic data: FTIR (U/cm−1): 2966 (w, υas(C–H) of CH3
group), 2877 (w, υs(C–H) of CH3 group), 2935 (m, υas(C–H) of CH2 group), 2829 (w-m,
υs(C–H) of CH2 group), 3076 (w, υ(C–H) aromatic), 2731 (w-m, υ(C–H) aldehydic), 1687
(s, υ(C=O)), 1597, 1575, and 1508 (s, m, m, υ(C=C) aromatic), 1253 (s, υ(C–O)), 1471 (m,
δ(C–H)).
4-butyloxybenzaldehyde (A4)
Yield = 80%. Characteristic spectroscopic data: FTIR (U/cm−1): 2976 (w, υas(C–H) of CH3
group), 2938 (w-m, υs(C–H) of CH3 group), 2959 (m, υas(C–H) of CH2 group), 2872 (w,

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
117
υs(C–H) of CH2 group), 3076 (w, υ(C–H) aromatic), 2731 (w-m, υ(C–H) aldehydic), 1688
(s, υ(C=O)), 1599, 1575, and 1508 (s, m, m, υ(C=C) aromatic), 1252 (s, υ(C–O)), 1468 (m,
δ(C–H)).
4-pentoxybenzaldehyde (A5)
Yield = 77%. Characteristic spectroscopic data: FTIR (U/cm−1): 2953 (w, υas(C–H) of CH3
group), 2872 (w, υs(C–H) of CH3 group), 2933 (m, υas(C–H) of CH2 group), 2862 (m, υs(C–
H) of CH2 group), 3070 (w, υ(C–H) aromatic), 2740 (w-m, υ(C–H) aldehydic), 1687 (s,
υ(C=O)), 1599, 1577, and 1508 (s, m, m, υ(C=C) aromatic), 1252 (s, υ(C–O)), 1467 (m,
δ(C–H)).
4-hexyloxybenzaldehyde (A6)
Yield = 65%. Characteristic spectroscopic data: FTIR (U/cm−1): 2953 (w-m, υas(C–H) of
CH3 group), 2870 (w, υs(C–H) of CH3 group), 2930 (m, υas(C–H) of CH2 group), 2859 (m,
υs(C–H) of CH2 group), 3073 (w, υ(C–H) aromatic), 2733 (w, υ(C–H) aldehydic), 1692 (s,
υ(C=O)), 1599, 1576, and 1508 (s, m, m, υ(C=C) aromatic), 1252 (s, υ(C–O)), 1470 (m,
δ(C–H)).
4-heptyloxybenzaldehyde (A7)
Yield = 70%. Characteristic spectroscopic data: FTIR (U/cm−1): 2956 (w-m, υas(C–H) of
CH3 group), 2867 (w, υs(C–H) of CH3 group), 2928 (m, υas(C–H) of CH2 group), 2857 (m,
υs(C–H) of CH2 group), 3075 (w, υ(C–H) aromatic), 2733 (w, υ(C–H) aldehydic), 1692 (s,
υ(C=O)), 1599, 1576, and 1508 (s, m, m, υ(C=C) aromatic), 1254 (s, υ(C–O)), 1468 (m,
δ(C–H)).
4-octyloxybenzaldehyde (A8)
Yield = 77%. Characteristic spectroscopic data: FTIR (U/cm−1): 2953 (w-m, υas(C–H) of
CH3 group), 2869 (w, υs(C–H) of CH3 group), 2926 (m, υas(C–H) of CH2 group), 2855 (m,
υs(C–H) of CH2 group), 3073 (w, υ(C–H) aromatic), 2733 (w, υ(C–H) aldehydic), 1692 (s,
υ(C=O)), 1599, 1576, and 1508 (s, m, m, υ(C=C) aromatic), 1254 (s, υ(C–O)), 1468 (m,
δ(C–H)).
4-nonyloxybenzaldehyde (A9)
Yield = 75%. Characteristic spectroscopic data: FTIR (U/cm−1): 2952 (w, υas(C–H) of CH3
group), 2870 (w, υs(C–H) of CH3 group), 2926 (s, υas(C–H) of CH2 group), 2852 (m, υs(C–
H) of CH2 group), 3074 (w, υ(C–H) aromatic), 2733 (w-m, υ(C–H) aldehydic), 1693 (s,
υ(C=O)), 1599, 1575, and 1508 (s, m, m, υ(C=C) aromatic), 1252 (s, υ(C–O)), 1467 (m,
δ(C–H)).
4-decyloxybenzaldehyde (A10)
Yield = 70%. Characteristic spectroscopic data: FTIR (U/cm−1): 2956 (w, υas(C–H) of CH3
group), 2869 (w, υs(C–H) of CH3 group), 2923 (s, υas(C–H) of CH2 group), 2852 (m, υs(C–H)

118
A. J. HAMMOOD ET AL.
of CH2 group), 3075 (w, υ(C–H) aromatic), 2733(w, υ(C–H) aldehydic), 1694 (s, υ(C=O)),
1599, 1576, and 1507 (s, m, m, υ(C=C) aromatic), 1251 (s, υ(C–O)), 1463 (m, δ(C–H)).
4-dodecyloxybenzaldehyde (A11)
Yield = 73%. Characteristic spectroscopic data: FTIR (U/cm−1): 2953 (w, υas(C–H) of CH3
group), 2872 (w, υs(C–H) of CH3 group), 2927 (s, υas(C–H) of CH2 group), 2850 (m, υs(C–H)
of CH2 group), 3060 (w, υ(C–H) aromatic), 2732 (w, υ(C–H) aldehydic), 1693 (s, υ(C=O)),
1599, 1576, and 1507 (s, m, m, υ(C=C) aromatic), 1252 (s, υ(C–O)), 1463 (m, δ(C–H)).
4-hexadecyloxybenzaldehyde (A12)
Yield = 89%, m.p. = 33–39°C. Characteristic spectroscopic data: FTIR (U/cm−1): 2948 (w,
υas(C–H) of CH3 group), 2868 (w, υs(C–H) of CH3 group), 2916 (s, υas(C–H) of CH2 group),
2849 (s, υs(C–H) of CH2 group), 3076 (w, υ(C–H) aromatic), 2733 (w, υ(C–H) aldehydic),
1688 (s, υ(C=O)), 1601, 1576, and 1507 (s, m, m, υ(C=C) aromatic), 1250 (s, υ(C–O)), 1471
(m, δ(C–H)).
4-octadecyloxybenzaldehyde (A13)
Yield = 79%, m.p. = 36–41°C. Characteristic spectroscopic data: FTIR (U/cm−1): 2960 (w,
υas(C–H) of CH3 group), 2864 (w, υs(C–H) of CH3 group), 2914 (s, υas(C–H) of CH2 group),
2850 (s, υs(C–H) of CH2 group), 3064 (w, υ(C–H) aromatic), 2732 (w, υ(C–H) aldehydic),
1692 (s, υ(C=O)), 1601, 1576, and 1507 (s, m, m, υ(C=C) aromatic),1254 (s, υ(C–O)), 1470
(m, δ(C–H)).
Synthesis of 1,2-bis[4-(n-alkoxy)benzylidene]hydrazine (general procedure) (B1–B13)
Hydrazine hydrate (0.125 g, 2.5 mmol) was added to a solution of appropriate 4-(n-
alkoxy)benzaldehyde (5 mmol) in ethanol (30 mL). Glacial acetic acid (0.1 mL) was then
added to the mixture. The reaction mixture was stirred for 1 h, during which a precipitate
was formed. This was removed by filtration, washed with cold water, recrystallized from a
proper solvent, and dried to give a pure compound. The purity of the compound was checked
by TLC using n-hexane: ethyl acetate (15:1) as eluents. The details of reaction conditions for
the preparation of each compound are summarized in Table 2.
1,2-bis(4-methoxybenzylidene)hydrazine (B1)
Yield = 62%. Elemental analysis (%) calc.: C 71.6, N 10.4, H 6.0; found: C 71.4, N 10.3, H
5.9. Characteristic spectroscopic data: FTIR (U/cm−1): 2987 (w, υas(C–H) of CH3 group),
2878 (w, υs(C–H) of CH3 group), 2922 (w, υas(C–H) of CH2 group), 2837 (m, υs(C–H) of
CH2 group), 3022 (w, υ(C–H) aromatic), 1620 (w, υ(C=N)), 1600, 1575, and 1508 (s, m, m,
υ(C=C) aromatic), 1249 (s, υ(C–O)), 1470 (m, δ(C–H)). UV-Vis (λ/nm): 230 (n–σ∗), 326
(π–π∗).1HNMR (δ/ppm): 3.73 (6H, t, OCH3), 6.97 (4H, d, J = 6.2 Hz, aromatic protons), 7.80
(4H, d, J = 6.2 Hz, aromatic protons), 8.63 (2H, s, CH=N). 13CNMR (δ/ppm): 56.11 (OCH3),
114.20 (aromatic C–H), 126.87 (aromatic C), 130.02 (aromatic C–H), 160.70 (CH=N), 162.30
(aromatic C–O). Mass spect. (m/z): 268.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
119
Table . Reaction conditions and quantities for the preparation of ,-bis[-(n-alkoxy)benzylidene]
hydrazine compounds.
Compound
-(n-alkoxy)benzaldehyde weight (g)
Recrystalizationnn solvent
Rf
Yield (%)
B
.
.
.
.

.
.
.
.
.
.
.
.
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Dichloromethane
Dichloromethane
Dichloromethane
Chloroform
Chloroform
.
.
.
.
.
.
.
.
.
.
.
.
.










B
B
B
B
B
B
B
B
B
B
B
B



1,2-bis(4-ethoxybenzylidene)hydrazine (B2)
Yield = 64%. Elemental analysis (%) calc.: C 73.0, N 9.5, H 6.8; found: C 72.8, N 9.4, H
6.7. Characteristic spectroscopic data: FTIR (U/cm−1): 2981 (s, υas(C–H) of CH3 group),
2896 (w-m, υs(C–H) of CH3 group), 2929 (s, υas(C–H) of CH2 group), 2852 (m, υs(C–H)
of CH2 group), 3030 (w, υ(C–H) aromatic), 1620 (w, υ(C=N)), 1600, 1577, and 1508 (s, m,
m, υ(C=C) aromatic), 1247 (s, υ(C–O)), 1473 (m, δ(C–H)). UV-Vis (λ/nm): 230 (n–σ∗),
330 (π–π∗). 1HNMR (δ/ppm): 1.45 (6H, t, CH3), 4.11 (4H, q, J = 4.0, OCH2), 6.96 (4H, d,
J = 6.1 Hz, aromatic protons), 7.78 (4H, d, J = 6.1 Hz, aromatic protons), 8.61 (2H, s, CH=N).
13CNMR (δ/ppm): 14.65 (CH3), 63.64 (OCH2), 114.84 (aromatic C–H), 127.11 (aromatic C),
130.05 (aromatic C–H), 160.66 (CH=N), 161.44 (aromatic C–O). Mass spect. (m/z): 296.
1,2-bis(4-propyloxybenzylidene)hydrazine (B3)
Yield = 60%. Elemental analysis (%) calc.: C 74.0, N 8.6, H 7.5; found: C 73.4, N 8.4, H 7.5.
Characteristic spectroscopic data: FTIR (U/cm−1): 2965 (w-m, υas(C–H) of CH3 group), 2882
(w, υs(C–H) of CH3 group), 2934 (w-m, υas(C–H) of CH2 group), 2876 (w-m, υs(C–H) of
CH2 group), 3069 (w, υ(C–H) aromatic), 1622 (m, υ(C=N)), 1597, 1572, and 1505 (s, m, s,
υ(C=C) aromatic), 1238 (s, υ(C–O)), 1460 (m, δ(C–H)). UV-Vis (λ/nm): 242 (n–σ∗), 331
(π–π∗). 1HNMR (δ/ppm): 1.08 (6H, t, CH3), 1.85 (4H, m, CH2), 4.00 (4H, t, OCH2), 6.97
(4H, d, J = 8.8 Hz, aromatic protons), 7.79 (4H, d, J = 9.1 Hz, aromatic protons), 8.63 (2H, s,
CH=N). 13CNMR (δ/ppm): 10.52 (CH3), 22.54 (CH2), 69.64 (OCH2), 114.75 (aromatic C–
H), 126.80 (aromatic C), 130.12 (aromatic C–H), 161.11 (CH=N), 161.62 (aromatic C–O).
Mass spect. (m/z): 324.
1,2-bis(4-butyloxybenzylidene)hydrazine (B4)
Yield = 61%. Elemental analysis (%) calc.: C 75.0, N 8.0, H 8.0; found: C 74.9, N 7.9, H 8.0.
Characteristic spectroscopic data: FTIR (U/cm−1): 2958 (s, υas(C–H) of CH3 group), 2875
(w-m, υs(C–H) of CH3 group), 2931 (m, υas(C–H) of CH2 group), 2855 (m, υs(C–H) of
CH2 group), 3025 (w, υ(C–H) aromatic), 1622 (w, υ(C=N)), 1599, 1567, and 1506 (s, m,
m, υ(C=C) aromatic), 1247 (s, υ(C–O)), 1465 (m, δ(C–H)). UV-Vis (λ/nm): 241 (n–σ∗),
332 (π–π∗). 1HNMR (δ/ppm): 0.97 (6H, t, CH3), 1.41 (4H, m, CH2), 1.85 (4H, m, CH2), 4.01
(4H, t, OCH2), 6.93 (4H, d, J = 9.0 Hz, aromatic protons), 7.75 (4H, d, J = 9.0 Hz, aromatic
protons), 8.61 (2H, s, CH=N). 13CNMR (δ/ppm): 14.41 (CH3), 21.40 (CH2), 30.84 (CH2)

120
A. J. HAMMOOD ET AL.
68.94 (OCH2), 114.30 (aromatic C–H), 127.20 (aromatic C), 130.33 (aromatic C–H), 161.10
(CH=N), 161.72 (aromatic C–O). Mass spect. (m/z): 352.
1,2-bis(4-pentyloxybenzylidene)hydrazine (B5)
Yield = 66%. Elemental analysis (%) calc.: C 75.8, N 7.4, H 8.5; found: C 75.5, N 7.2, H
8.4. Characteristic spectroscopic data: FTIR (U/cm−1): 2951 (w-m, υas(C–H) of CH3 group),
2872 (w, υs(C–H) of CH3 group), 2934 (m, υas(C–H) of CH2 group), 2854 (m, υs(C–H) of
CH2 group), 3066 (w, υ(C–H) aromatic), 1622 (m, υ(C=N)), 1599, 1568, and 1506 (m, s,
s, υ(C=C) aromatic), 1248 (s, υ(C–O)), 1466 (m, δ(C-H)). UV-Vis (λ/nm): 241 (n–σ∗), 331
(π–π∗). 1HNMR (δ/ppm): 0.97 (6H, t, CH3), 1.27–1.55 (8H, m, CH2), 1.84 (4H, m, CH2), 4.02
(4H, t, OCH2), 6.97 (4H, d, J = 9.1 Hz, aromatic protons), 7.80 (4H, d, J = 9.1 Hz, aromatic
protons), 8.64 (2H, s, CH=N). 13CNMR (δ/ppm): 14.04 (CH3), 22.48 (CH2), 28.19 (CH2),
28.90 (CH2), 68.15 (OCH2), 161.08 (CH=N), 114.76 (aromatic C–H), 126.79 (aromatic C),
130.13 (aromatic C–H), 161.08 (CH=N), 161.64 (aromatic C–O). Mass spect. (m/z): 380.
1,2-bis(4-hexyloxybenzylidene)hydrazine (B6)
Yield = 62%. Elemental analysis (%) calc.: C 76.4, N 6.9, H 8.9; found: C 76.3, N 6.8, H
8.8. Characteristic spectroscopic data: FTIR (U/cm−1): 2954 (w, υas(C–H) of CH3 group),
2924 (m, υs(C–H) of CH3 group), 2940 (w, υas(C–H) of CH2 group), 2857 (m, υs(C–H) of
CH2 group), 3050 (w, υ(C–H) aromatic), 1618 (s, υ(C=N)), 1605, 1572, and 1508 (s, m, m,
υ(C=C) aromatic), 1242 (s, υ(C–O)), 1466 (m, δ(C–H)). UV-Vis (λ/nm): 229 (n–σ∗), 329
(π–π∗). 1HNMR (δ/ppm): 0.90 (6H, t, CH3), 1.37–1.46 (12H, m, CH2), 1.84 (4H, m, CH2),
4.0 (4H, t, OCH2), 6.94 (4H, d, J = 8.9 Hz, aromatic protons), 7.76 (4H, d, J = 8.8 Hz, aromatic
protons), 8.60 (2H, s, CH=N). 13CNMR (δ/ppm): 14.16 (CH3), 22.72 (CH2), 25.82 (CH2),
29.28 (CH2), 31.70 (CH2), 68.28 (OCH2), 114.86 (aromatic C–H), 126.91 (aromatic C), 130.22
(aromatic C–H), 161.21 (CH=N), 161.74 (aromatic C–O). Mass spect. (m/z): 408.
1,2-bis(4-heptyloxybenzylidene)hydrazine (B7)
Yield = 64%. Elemental analysis (%) calc.: C 77.0, N 6.4, H 9.2; found: C 77.1, N 6.3, H
9.1. Characteristic spectroscopic data: FTIR (U/cm−1): 2953 (m, υas(C–H) of CH3 group),
2874 (w-m, υs(C–H) of CH3 group), 2922 (m, υas(C–H) of CH2 group), 2857 (m, υs(C–H)
of CH2 group), 3055 (w, υ(C–H) aromatic), 1622 (s, υ(C=N)), 1602, 1574, and 1508 (s, m,
m, υ(C=C) aromatic), 1246 (s, υ(C–O)), 1466 (m, δ(C-H)). UV-Vis (λ/nm): 229 (n–σ∗), 330
(π–π∗). 1HNMR (δ/ppm): 0.96 (6H, t, CH3), 1.29–1.49 (16H, m, CH2), 1.83 (4H, m, CH2), 4.0
(4H, t, OCH2), 6.94 (4H, d, J = 8.9 Hz, aromatic protons), 7.81 (4H, d, J = 8.9 Hz, aromatic
protons), 8.59 (2H, s, CH=N). 13CNMR (δ/ppm): 14.01 (CH3), 23.10 (CH2), 26.60 (CH2),
30.0 (CH2), 32.50 (CH2), 69.11 (OCH2), 114.30 (aromatic C–H), 127.21 (aromatic C), 130.02
(aromatic C–H), 161.10 (CH=N), 161.66 (aromatic C–O). Mass spect. (m/z): 436.
1,2-bis(4-octyloxybenzylidene)hydrazine (B8)
Yield = 60%. Elemental analysis (%) calc.: C 77.5, N 6.0, H 9.5; found: C 77.4, N 5.9, H 9.4.
Characteristic spectroscopic data: FTIR (U/cm−1):2938 (w-m, υas(C–H) of CH3 group), 2862
(w-m, υs(C–H) of CH3 group), 2920 (m, υas(C–H) of CH2 group), 2847 (m, υs(C–H) of CH2
group), 3051 (w, υ(C–H) aromatic), 1616 (s, υ(C=N)), 1603, 1570, and 1508 (s, m, s, υ(C=C)

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
121
Figure . FTIR spectra of (A) and (B).
aromatic), 1246 (s, υ(C–O)), 1470 (m, δ(C–H)). UV-Vis (λ/nm): 229 (n–σ∗), 332 (π–π∗).
1HNMR (δ/ppm): 0.90 (6H, t, CH3), 1.28–1.45 (20H, m, CH2), 1.84 (4H, m, CH2), 4.0 (4H, t,
OCH2), 6.95 (4H, d, J = 8.8 Hz, aromatic protons), 7.80 (4H, d, J = 8.8 Hz, aromatic protons),
8.61 (2H, s, CH=N). 13CNMR (δ/ppm): 14.24 (CH3), 22.79 (CH2), 26.15 (CH2), 29.32 (CH2),
29.48 (CH2), 31.95 (CH2), 68.29 (OCH2), 114.87 (aromatic C–H), 126.91 (aromatic C), 130.22
(aromatic C–H), 161.21 (CH=N), 161.74 (aromatic C–O). Mass spect. (m/z): 464.
1,2-bis(4-nonyloxybenzylidene)hydrazine (B9)
Yield = 64%. Elemental analysis (%) calc.: C 78.0, N 5.7, H 9.8; found: C 77.8, N 5.6, H 9.7.
Characteristic spectroscopic data: FTIR (U/cm−1): 2953 (m, υas(C–H) of CH3 group), 2860
(w, υs(C–H) of CH3 group), 2922 (s, υas(C–H) of CH2 group), 2848 (m, υs(C–H) of CH2
group), 3070 (w, υ(C–H) aromatic), 1622 (s, υ(C=N)), 1600, 1574, and 1508 (s, m, s, υ(C=C)
aromatic), 1250 (s, υ(C–O)), 1470 (m, δ(C–H)). UV-Vis (λ/nm): 229 (n–σ∗), 332 (π–π∗).
1HNMR (δ/ppm): 0.91 (6H, t, CH3), 1.31–1.49 (24H, m, CH2), 1.83 (4H, m, CH2), 4.03 (4H, t,
OCH2), 6.97 (4H, d, J = 8.8 Hz, aromatic protons), 7.79 (4H, d, J = 8.8 Hz, aromatic protons),
8.64 (2H, s, CH=N). 13CNMR (δ/ppm): 14.13 (CH3), 22.69 (CH2), 26.03 (CH2), 29.28 (CH2),
29.54 (CH2), 31.89 (CH2), 68.19 (OCH2), 114.76 (aromatic C–H), 126.73 (aromatic C), 130.14
(aromatic C–H), 161.11 (CH=N), 161.67 (aromatic C–O). Mass spect. (m/z): 492.
1,2-bis(4-decyloxybenzylidene)hydrazine (B10)
Yield = 61%. Elemental analysis (%) calc.: C 78.4, N 5.4, H 10.1; found: C 78.1, N 5.3, H
10.1. Characteristic spectroscopic data: FTIR (U/cm−1): 2955 (w-m, υas(C–H) of CH3 group),
2872 (w, υs(C–H) of CH3 group), 2918 (s, υas(C–H) of CH2 group), 2851 (m, υs(C–H) of
CH2 group), 3069 (w, υ(C–H) aromatic), 1624 (m, υ(C=N)), 1605, 1575, and 1508 (m, m, m,

122
A. J. HAMMOOD ET AL.
Figure . NMR spectra of (B): (a) HNMR spectrum, (b) CNMR spectrum.
υ(C=C) aromatic), 1248 (s,υ(C–O)), 1464 (m, δ(C–H)). UV-Vis (λ/nm): 230 (n–σ∗), 330 (π–
π∗).1HNMR (δ/ppm): 0.98 (6H, t, CH3), 1.30–1.48 (28H, m, CH2), 1.81 (4H, m, CH2), 4.03
(4H, t, OCH2), 6.95 (4H, d, J = 8.9 Hz, aromatic protons), 7.80 (4H, d, J = 8.9 Hz, aromatic
protons), 8.63 (2H, s, CH=N). 13CNMR (δ/ppm): 14.07 (CH3), 23.28 (CH2), 26.66 (CH2),
29.47 (CH2), 30.14 (CH2), 31.94 (CH2), 68.08 (OCH2), 114.44 (aromatic C–H), 126.89 (aro-
matic C), 129.81 (aromatic C–H), 161.24 (CH=N), 161.69 (aromatic C–O). Mass spect. (m/z):
520.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
123
Table . Phase transition temperatures and thermodynamic data for ,-bis[-(n-alkoxy)benzylidene]
hydrazine compounds determined by DSC.
Phase transitions T°C (ꢀH/KJ.mol−
(ꢀS/J.mole−.K−) on first heating
)
Phase transitions T°C (ꢀH/KJ.mol−
(ꢀS/J.mole−.K−) on first cooling
)
Compound
n



B
B
B
Cr–N . (.) [.]
N–I . (.) [.]
Cr–Cr . (.) [.]
Cr–N–I . (.) [.]
Cr–Cr . (.) [.]
Cr-N . (.) [.]
N-I  (.) [.]
I–N . (−.) [−.]
N–Cr . (−.) [−.]
I–N . (−.) [−.]
N–Cr–Cr . (−.) [−.]
I–N . (−.) [−.]
N–Cr . (−.) [−.]
Cr–Cr . (−.) [−.]
I–N . (−.) [−.]
B

Cr–Cr–N  (.) [.]
N–I . (.) [.]
N–Cr . (−.) [−.]
Cr–Cr . (−.) [−.]
I–N . (−.) [−.]
B
B

Cr–Cr–Cr . (.) [.]
Cr–SmC–N . (.) [.]
N–I . (.) [.]
N–SmC–Cr . (−.) [−.]
Cr–Cr–Cr . (−.) [.]
I–ND . (−.) [−.]
ND–NTh . (−.) [−.]
 Cr–Cr–Cr . (.) [.]
Cr–SmC–N  (.) [.]
N–I . (.) [.]
N
Th–SmC–Cr . (−.) [−.]
Cr–Cr–Cr . (−.) [−.]
I–N–SmA . (−.) [−.]
SmA–Cr–Cr . (−.) [−.]
Cr–Cr–Cr . (−.) [−.]
I–N–SmA . (−.) [−.]
SmA–Cr–Cr . (−.) [−.]
Cr–Cr–Cr . (−.) [−.]
I–ND . (−.) [−.]
B
B
B
 Cr–Cr–Cr . (.) [.]
Cr– Cr–SmA . (.) [.]
SmA–N–I . (.) [.]
 Cr-Cr-Cr . (.) [.]
Cr-Cr. (.) [.]
Cr–SmA–N–I . (.) [.]
 Cr–Cr–Cr-Cr . (.) [.]
Cr–SmA–N–I .(.) [.]
ND–NTh . (−.) [−.]
NTh–SmA–Cr . (−.) [−.]
Cr-Cr–Cr–Cr . (−.) [−.]
Cr: crystalline solid, SmA: smectic A mesophase, SmC: smectic C mesophase, ND: nematic droplets-like texture, NTh: nematic
thread-like texture, I: isotropic liquid, n: alkyl chain length.
1,2-bis(4-dodecyloxybenzylidene)hydrazine (B11)
Yield = 66%. Elemental analysis (%) calc.: C 79.1, N 4.9, H 10.5; found: C 79.0, N 4.7, H 10.4.
Characteristic spectroscopic data: FTIR (U/cm−1): 2955 (w-m, υas(C–H) of CH3 group), 2872
(w, υs(C–H) of CH3 group), 2916 (s, υas(C–H) of CH2 group), 2849 (m, υs(C–H) of CH2
group), 3069 (w, υ(C–H) aromatic), 1622 (m, υ(C=N)), 1605, 1574, and 1508 (m, m, m,
υ(C=C) aromatic), 1250 (s, υ(C–O)), 1470 (m, δ(C–H)). UV-Vis (λ/nm): 228 (n–σ∗), 329
(π–π∗).1HNMR (δ/ppm): 0.97 (6H, t, CH3), 1.29–1.45 (36H, m, CH2), 1.80 (4H, m, CH2),
4.02 (4H, t, OCH2), 6.94 (4H, d, J = 8.8 Hz, aromatic protons), 7.81 (4H, d, J = 8.8 Hz,
aromatic protons), 8.62 (2H, s, CH=N). 13CNMR (δ/ppm): 14.05 (CH3), 23.25 (CH2), 26.69
(CH2), 29.44 (CH2), 30.11 (CH2), 31.92 (CH2), 68.07 (OCH2), 114.41 (aromatic C–H), 126.89
(aromatic C), 129.79 (aromatic C–H), 161.22 (CH=N), 161.61 (aromatic C–O). Mass spect.
(m/z): 576.
1,2-bis(4-hexadecyloxybenzylidene)hydrazine (B12)
Yield = 64%. Elemental analysis (%) calc.: C 80.2, N 4.1, H 11.1; found: C 80.0, N 4.0, H
11.1. Characteristic spectroscopic data: FTIR (U/cm−1): 2955 (w-m, υas(C–H) of CH3 group),
2872 (w, υs(C–H) of CH3 group), 2916 (s, υas(C–H) of CH2 group), 2847 (s, υs(C–H) of
CH2 group), 3070 (w, υ(C–H) aromatic), 1624 (m, υ(C=N)), 1607, 1575, and 1510 (m, m,
m, υ(C=C) aromatic), 1252 (s, υ(C–O)), 1462 (m, δ(C–H)). UV-Vis (λ/nm): 229 (n–σ∗),
1
329 (π–π∗). HNMR (δ/ppm): 0.96 (6H, t, CH3), 1.29–1.42 (52H, m, CH2), 1.81 (4H, m,

124
A. J. HAMMOOD ET AL.
Figure . DSC curves for (a) B and (b) B at a rate of .°C/min, red line is the heating cycle, while blue line
is the cooling cycle.
CH2), 4.01 (4H, t, OCH2), 6.92 (4H, d, J = 8.8 Hz, aromatic protons), 7.80 (4H, d, J = 8.8 Hz,
aromatic protons), 8.60 (2H, s, CH=N). 13CNMR (δ/ppm): 14.0 (CH3), 23.12 (CH2), 26.65
(CH2), 29.23 (CH2), 30.01 (CH2), 31.88 (CH2), 68.06 (OCH2), 114.35 (aromatic C–H), 126.84
(aromatic C), 129.73 (aromatic C–H), 161.12 (CH=N), 161.55 (aromatic C–O). Mass spect.
(m/z): 688.
1,2-bis(4-octadecyloxybenzylidene)hydrazine (B13)
Yield = 66%. Elemental analysis (%) calc.: C 80.6, N 3.8, H 11.4; found: C 80.5, N 3.7, H
11.3. Characteristic spectroscopic data: FTIR (U/cm−1): 2955 (w-m, υas(C–H) of CH3 group),

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
125
Figure . (a) Nematic thread-like texture of B at °C upon cooling. (b) Nematic thread-like texture of B at
°C upon heating. (c) Nematic droplets-like texture of B at °C upon cooling. (d) Nematic droplets-like
texture of B at °C upon cooling. (e) SmA mesophase of B at °C upon cooling. (f) SmC mesophase of
B at °C upon cooling.
2872 (w, υs(C–H) of CH3 group), 2916 (s, υas(C–H) of CH2 group), 2847 (s, υs(C–H) of
CH2 group), 3069 (w, υ(C–H) aromatic), 1624 (m, υ(C=N), 1607, 1576, and 1510 (m, m, m,
υ(C=C) aromatic), 1252 (s, υ(C–O)), 1462 (m, δ(C–H)). UV-Vis (λ/nm): 230 (n–σ∗), 330
(π–π∗).1HNMR (δ/ppm): 0.96 (6H, t, CH3), 1.28–1.40 (60H, m, CH2), 1.80 (4H, m, CH2),
4.0 (4H, t, OCH2), 6.90 (4H, d, J = 9.0 Hz, aromatic protons), 7.75 (4H, d, J = 9.0 Hz, aromatic
protons), 8.58 (2H, s, CH=N). 13CNMR (δ/ppm): 14.0 (CH3), 23.10 (CH2), 26.60 (CH2), 29.17

126
A. J. HAMMOOD ET AL.
Figure . Transition temperatures as a function of alkyl chain length for ,-bis[-(n-alkoxy)benzylidene]
hydrazine compounds.
(CH2), 29.80 (CH2), 31.77 (CH2), 68.02 (OCH2), 114.30 (aromatic C–H), 126.73 (aromatic
C), 129.60 (aromatic C–H), 161.01 (CH=N), 161.43 (aromatic C–O). Mass spect. (m/z): 744.
Result and discussion
Synthesis and characterization of the compounds
The present study reports a convenient and high-yielding protocol for the synthesis of 1,2-
bis[4-(n-alkoxy)benzylidene]hydrazine compounds (where, n-alkoxy: O(CH2)nH, n = 1, 2,
3, 4, 5, 6, 7, 8, 9, 10, 12, 16, or 18). The synthesis was made in two stages (Scheme 1):
(i) Alkylation of the OH group of 4-hydroxybenzaldehyde using the Williamson method to
obtain 4-(n-alkoxy) benzaldehydes.
(ii) Condensation reaction of hydrazine hydrate and appropriately 4-(n-alkoxy) benzaldehyde
compounds (mole ratio (1:2) respectively) in acidic medium under ambient conditions.
The prepared organic compounds have been characterized and their structures were elu-
cidated depending upon micro-elemental analysis and spectral data (IR, UV-Vis, 1HNMR,
13C{1H}NMR, 2D 1H-1H-cozy, 2D 1H-13C- HSQC, and mass spectra).
Fourier transform infrared spectroscopy (FTIR) spectra of 1,2-bis[4-(n-
alkoxy)benzylidene]hydrazine compounds (B1–B13) showed characteristic bands due to
C–H, C=C, C=N, and C–O functional groups [25]; for details, see Experimental part.
Furthermore, the FTIR spectra of these compounds were compared with that of the corre-
sponding 4-(n-alkoxy) benzaldehyde compounds (A1–A13). Because of this comparison, the
following aspects have been observed (for the comparison, see Figure 1):
(i) Appearance of a new band in all spectra of 1,2-bis[4-(n-alkoxy)benzylidene]hydrazine
compounds (B1–B13) in the range: (1616–1624 cm−1), which can be assigned to the stretch-
ing vibration of (C=N) group.
(ii) The bands related to the υ(C–H) aldehydic and υ(C=O) groups that observed in the
spectra of 4-(n-alkoxy) benzaldehyde compounds (A1–A13) in the ranges (2729–2740
cm−1) and (1680–1694 cm−1), respectively, were disappeared in the spectra of 1,2-bis[4-
(n-alkoxy)benzylidene]hydrazine compounds (B1–B13).

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
127
Scheme . Synthetic diagram for the preparation of ,-bis[-(n-alkoxy)benzylidene]hydrazine compounds.
These facts might indicate the formation of azine compounds.
The 1HNMR and 13C{1H}NMR spectra of the prepared compounds, displayed signals cor-
responding to the various proton and carbon nuclei (for further details, see Experimental
section and for instant example, see Figure 2). The assignments of the chemical shifts in both
1HNMR and 13C{1H}NMR spectra of these compounds are supported by the 2D spectra (1H-
1H-cozy and 1H-13C- HSQC NMR spectra).
Liquid crystalline behavior of the compounds
Liquid crystalline behavior of the prepared organic compounds: 1,2-bis[4-(n-
alkoxy)benzylidene]hydrazine was studied using polarized light optical microscopy (POM)
and differential scanning calorimetry (DSC) techniques. The phase transition temperatures
and thermodynamic data are summarized in Table 3 (the temperatures determined are peak
temperatures). All of these compounds displayed enantiotropic LC properties. Smectic and
nematic mesophases could be observed for the compounds: B9–B13, while only nematic
mesophase is detected for B1–B8.

128
A. J. HAMMOOD ET AL.
The DSC thermograms of B2, B4, B5, B9, B10, and B11 show intense melting peaks (mainly
due to transitions from crystal solid phases into nematic mesophase) followed by a weak
clearing peak at higher temperatures (transition from nematic mesophase to the isotropic),
examples are shown in Figure 3. No separated weak clearing peak could be noticed in the
thermograms of B12 and B13 compounds, and instead an intense peak appeared. This could
be attributed to phase transition from the more ordered mesophase (crystalline solid) to
the isotropic, passing through smectic and nematic mesophases. Successive heat–cool cycles
reproduce the same behavior. In the compounds of long length chain (B11, B12, and B13), the
phase transitions in both heating and cooling were found to be very close to each other. This is
not true for rest of the compounds. Observation of the textures under microscope confirmed
the liquid crystalline behavior (examples are shown in Figure 4). Upon cooling of all of the
prepared compounds from the isotropic phase, nematic droplets-like texture were formed.
These droplets joined together to give nematic thread-like texture [26]. Another element that
confirms the identity of nematic mesophase is the transition enthalpy of the clearing point of
compounds B2, B3, B4, B5, B9, and B10. The enthalpy being 0.59–2.04 KJ mol−1. This is typical
for nematic to isotropic transition [27–28]. Typical fan-shaped texture of a SmA mesophase
has been shown by the compounds B11, B12, and B13, while a texture of SmC was exhibited by
B9 and B10 compounds. As could be seen in Table 3, all compounds showed crystalline poly-
morphism. These solid-state transitions were observed by POM and confirmed by DSC. The
phase behavior of our compounds is consistent with literature data on similar compounds
[16, 17].
Increasing alkyl chain length may have different effects on the melting point. In general,
increasing the chain length can increase the van der Waals interactions and therefore may
increase the melting point. On the other hand, the flexibility of the alkyl chain tends to disrupt
the lateral core–core interactions and therefore reduces the melting point. The effect of chain
length on the melting point may thus vary from compound to compound of different core
systems. Because the melting temperatures of these azine compounds decrease with increasing
chain length, the melting process appears to be governed by the random motion of chains but
is less affected by the van der Waals interactions between chains [29–31]. A plot of transition
temperature values as a function of the length of terminal alkoxy chain for these compounds
is shown in Figure 5, which shows odd-even effect. The effect being more pronounced for
shorter terminal chains.
Acknowledgments
We thank Dr. Adnan Ibraheem Al-Saadi, Kerbala University, and Dr Dhafir Tamween Al-Hetemi, Bagh-
dad University, for their help. We are indebted to Arab Science of Technology Foundation (ASTF) for
their support.
References
[1] Smith, M. B., & March, J. (2007). March’s Advanced Organic Chemistry Reactions, Mechanisms and
Structure, 6th Edn. Wiley Interscience: New Jersey.
[2] Safari, J., & Gandomi-Ravandi, S. (2011). Syth. Commun., 41, 645–651.
[3] Yang, Z., Zheng, J., & Yang, C. (2004). Lanzhou Daxue Xuebao Ziran Kexueban, 40, 51.
[4] Hoelzemann, G. (2006). Expert Opin. Ther. Pat., 16, 1175.
[5] Dragancea, D., Arion, V. B., Shova, S., Rentschler, E., & Gerbeleu, N. V. (2005). Angew. Chem., 44,
7938–7942.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
129
[6] Rajeswaran, M., Blanton, T. N., Giesen, D. J., Whitcomb, D. R., Zumbulyadis, N., et al. (2006). J.
Solid State Chem., 179, 1053–1059.
[7] Wu,, C. Y., Chen,, Y., Jing,, S. Y., Lee,, C. S., Dinda,, J., & Hwang,, W. S. (2006). Polyhedron, 25,
3053–3065.
[8] Greene,, T. W., & Wuts,, P. G. (1999). Protective Groups in Organic Synthesis, 2nd Edn., Wiley: New
York, NY.
[9] Machado, H. J. S., & Hinchliffe, A. (1995). J. Mol. Struct., 339, 255–258.
[10] Khoshkhoo, S., & Anwar, J. (1993). J. Phys. D, 26, B90–B93.
[11] Rizzo, P., Albunia, A. R., & Guerra, G. (2005). Polymer, 46, 9549–9554.
[12] Chen, J., Shao, M., Xiao, K., Rondinone, A. J., Loo, Y-L., et al. (2014). Nanoscale, 6, 449–456.
[13] Demus, D., Goodby, J., Gray, G. W., Spiess, H.-W., & Vill, V. (1998). Handbook of Liquid Crystals,
Vol. 2a, Wiley-VCH: Weinheim, Germany.
[14] Wilfrid, G. S., & Glenn, H. B. (1959). J. Am. Chem. Soc., 81, 2532–2537.
[15] Deun, R. V., Parac-Vogt, T. N., Van Hecke, K., Van Meervelt, L., Binnemans, K., et al. (2003). J.
Mater. Chem., 13, 1639–1645.
[16] Artigas, M., Marcos, M., Melendez, E., & Serrano, J. L. (1985). Mol. Cryst. Liq. Cryst., 130, 337–347.
[17] Marcos, M., Melendez, E., & Serrano, J. L. (1983). Mol. Cryst. Liq. Cryst., 91, 157–172.
[18] Centore, R., Capitolino, V., Cerciello, F., Tuzi, A., Borbone, F., et al. (2015). Cryst. Eng. Comm., 17,
8864–8869.
[19] Wei, Q., Shi, L., Cao, H., Yang, H., & Wang, Y. B. (2007). Chinese Chem. Lett., 18, 527–529.
[20] Espinet, P., Lalinde, E., Marcos, M., Perez, J., & Serrano, J. L. (1990). Organometallics, 9(3),
555–560.
[21] Takatsu, H., Takehara, S., Takeuchi, K., Negishi, M., Osawa, et al. (2000). US Patent No.
006010642A.
[22] Runti, C., Collino, F., & Pescani, G. (1968). Farmaco. Ed. Sci., 23, 114.
[23] Yeap, G.-Y., Takanishi, Y., & Takezoe, H. (2000). Spectroscopy, 14, 93–98.
[24] Yeap, G.-Y., Ha, S.-T., Ito, M. M., Boey, P.-L., & Mahmood, W. A. K. (2004). J. Mol. Struct., 687,
57–64.
[25] Silverstein, R., Webster, F., & Kiemle, D. (2005). Spectrophotometric Identification of Organic Com-
pounds, 7th Edn., John Willy: New York, NY.
[26] Demus, D., & Richter, L. (1978). Textures of Liquid Crystals, 1st Edn., Verlag: Weinheim, Germany.
[27] Collings, P. J., Gray, G. W., Goodby, J. W., & Hird, M. (1997). Introduction to Liquid Crystals, 1st
Edn., Taylor & Francis: London.
[28] Kumar, S. (2001). Liquid Crystals, Experimental Study of Physical Properties and Phase Transitions,
1st Edn., Cambridge University Press: Cambridge, UK.
[29] Sluckin, T. J., Dunmur, D. A., & Stegemeyer, H. (2004). Crystals That Flow – Classic Papers From
the History of Liquid Crystals, Taylor & Francis: London.
[30] Demus, D., Goodby, J. Gray, & George, W. (1998). Handbook of Liquid Crystals, Wiley-VCH:
Weinheim, Germany, 1–3.
[31] Lee, C. K., Hsu, K.-M., Tsai, C.-H., Lai, C. K., & Lin, I. J. B. (2004). Dalton Trans., 1120–1126.