Synthesis and mesomorphic properties of new columnar liquid crystal containing 1,3,5-triiminebenzene with pendant 1,3,4-thiadiazole Group

Article abstract of DOI:10.1080/15421406.2013.864546

A novel discotic liquid crystal series based on 1,3,5-benzenetrisazomethine derivatives with three pendant 2-amino-5-(4′-n-alkoxy)phenyl-1,3,4- thiadiazole has been synthesized, which is the first columnar molecules containing 1,3,4-thiadiazole moiety exhibiting a discotic liquid crystal. The molecular structure of compounds was confirmed by FT-IR, ¹H-NMR, and mass spectroscopy and elemental analysis. The electron excitation properties of these compounds were investigated by UV-vis absorption spectroscopy. Their liquid crystalline properties were studied by polarizing optical microscopy and differential scanning calorimetry. The formation of a columnar mesophase was found to be dependent on the number of methylene unit in alkoxy side chains.

Full text of DOI:10.1080/15421406.2013.864546

This article was downloaded by: [Memorial University of Newfoundland]
On: 01 August 2014, At: 19:11
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
Synthesis and Mesomorphic Properties of
New Columnar Liquid Crystal Containing
1,3,5-triiminebenzene with Pendant
1,3,4-thiadiazole Group
Mustafa K. S. Al-Malkia, Ayad S. Hameedb & Ammar H. Al-Dujailic
a Department of Chemistry, College of Education for Science,
University of Diyala, Diyala, Iraq
b Department of Chemistry, College of Science, University of Tikrit,
Tikrit, Iraq
c Department of Chemistry, College of Education for Pure Science,
Ibn Al-Haytham, University of Baghdad, Baghdad, Iraq
Published online: 27 May 2014.
To cite this article: Mustafa K. S. Al-Malki, Ayad S. Hameed & Ammar H. Al-Dujaili (2014) Synthesis
and Mesomorphic Properties of New Columnar Liquid Crystal Containing 1,3,5-triiminebenzene
with Pendant 1,3,4-thiadiazole Group, Molecular Crystals and Liquid Crystals, 593:1, 34-42, DOI:
10.1080/15421406.2013.864546
To link to this article: http://dx.doi.org/10.1080/15421406.2013.864546
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. 593: pp. 34–42, 2014
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2013.864546
Synthesis and Mesomorphic Properties of New
Columnar Liquid Crystal Containing
1,3,5-triiminebenzene with Pendant
1,3,4-thiadiazole Group
MUSTAFA K. S. AL-MALKI,1 AYAD S. HAMEED,2
AND AMMAR H. AL-DUJAILI3,∗
1Department of Chemistry, College of Education for Science, University of
Diyala, Diyala, Iraq
2Department of Chemistry, College of Science, University of Tikrit, Tikrit, Iraq
3Department of Chemistry, College of Education for Pure Science, Ibn
Al-Haytham, University of Baghdad, Baghdad, Iraq
A novel discotic liquid crystal series based on 1,3,5-benzenetrisazomethine deriva-
tives with three pendant 2-amino-5-(4ꢀ-n-alkoxy)phenyl-1,3,4-thiadiazole has been
synthesized, which is the first columnar molecules containing 1,3,4-thiadiazole moi-
ety exhibiting a discotic liquid crystal. The molecular structure of compounds was
confirmed by FT-IR, 1H-NMR, and mass spectroscopy and elemental analysis. The elec-
tron excitation properties of these compounds were investigated by UV-vis absorption
spectroscopy. Their liquid crystalline properties were studied by polarizing optical mi-
croscopy and differential scanning calorimetry. The formation of a columnar mesophase
was found to be dependent on the number of methylene unit in alkoxy side chains.
Keywords Columnar phase; liquid crystals; Schiff base; thiadiazole
Introduction
Discotic liquid crystal molecules have flat or nearly flat cores surrounded by six or eight
(sometimes four) long chain substituents. The first discotic liquid crystal were observed
in the hexa-alkanoyloxybenzenes and the hexaalkoxy- and alkanoyloxy-triphenylenes and
was found in 1977 by the Indian researcher Chandrasekhar [1]. Since then, a large number
of discoid mesogenic compounds have been discovered in which triphenylene, porphyrin,
phthalocyanine, coronene, and other aromatic molecules [2,3] are involved.
Many a new discotic liquid crystals have been developed to induce functions such as
improved charge transportation [4,5], anisotropic ion transportation [6–8], gas and molec-
ular separation [9], photonics [10], and biological [11] functions.
During the last decades many series of liquid crystalline compounds containing hete-
rocyclic groups have been synthesized due to their potentially wide range of applications,
∗Address correspondence to Ammar H. Al-Dujaili, Department of Chemistry, College of Educa-
tion for Pure Science, Ibn Al-Haytham, University of Baghdad, Baghdad, Iraq. E-mail: ammar.h.s.@
ihcoedu.uobaghdad.edu.iq
34

Synthesis and Mesomorphic Properties of New Columnar LC
35
such as in the optical, electrical, and biological medical fields [12–15]. Among these hetero-
cyclic, 1,3,4-thiadiazole derivatives have been studied as excellent candidates for material
applications due to their excellent thermal and chemical stabilities, their electron-deficient
nature and good electron accepting ability [16,17]. Numerous examples of these based
compounds have been applied as electron-transporting materials [18]. On the other hand,
most examples of mesomorphic 1,3,4-oxadiazole derivatives were generally calamitic liq-
uid crystals exhibiting nematic/smectic phases [19–31] and electron-transporting capability
[32–35].
Limited number of discotic 1,3,4-oxadiazole derivatives have been reported [36–47].
For example, a novel three-armed discotic liquid crystal based on 1,3,5-triethynylbenzene as
a core and 2,5-diphenyloxadiazole as rigid arms has been synthesized, which is the first star-
shaped molecule exhibiting a discotic nematic phase [43]. A new class of discotics derived
from tris(N-salicylideneaniline) with outer 1,3,4-oxadiazole wings have been synthesized
and their thermal and photophysical properties are investigated by Yelamaggad et al. [44].
A novel discotic liquid crystalline material composed of 1,3,5-tri-substituted benzene core
and 2-(4-hexloxyphenyl)-oxadiazole-5-yl arms was synthesized and characterized by Kim
et al. [45]. Lai et al. reported a series of polycatenar 2,5-bis (3,4,5-trialkoxyphenyl)-1,3,4-
oxadiazoles [37] and their corresponding palladium(II) complexes (metallomesogens) [38],
which showed columnar phases, and some of them were room temperature liquid crystals.
Recently, columnar liquid crystalline materials based on 1,3,5-benzenetrisamide derivatives
with three pendant 2-phenyl-5-(mono-, di-, and/or tri-n-alkoxyphenyl)-1,3,4-oxadiazole
arms were reported by Barbera et al. [46]. A series of hexacatenar columnar liquid crystals
containing the 1,3,4-oxadiazole group as a rigid core were reported by Li et al. [39,42].
A lollipop-shaped molecule containing 1,3,4-oxadiazole moieties display columnar phase
was designed and synthesized by Choi et al. [47].
As mentioned above most of the reported heterocyclic compounds display columnar
mesophase containing 1,3,4-oxadiazole. Recently, Parra et al. [48] reported the synthesis of
columnar liquid crystals based on amino-1,3,4-thiadiazole derivatives. Thus we designed
and synthesized a novel discotic liquid crystalline composed of 1,3,5-triiminebenzene and
three identical arms containing 1,3,4-thiadiazole moiety. To the best of our knowledge,
there have been no reports on the mesomorphic behavior of discotic columnar liquid
crystals containing 1,3,4-thiadiazole derivatives.
Experimental
General
All the chemicals were supplied from Aldrich-Sigma Chemicals Co. and used as received.
FTIR spectra were recorded using potassium bromide discs on a 8400s Shimadzu spec-
1
trophotometer. The H NMR spectra were recorded on Bruker AMX-300 spectrometer
at 300 MHz, using deutrated chloroform or DMSO as solvent with TMS as an internal
standard. Elemental analysis (C,H,N) were carried out using a Perkin-Elmer model 2400
instrument. Mass spectra were recorded on IEOL JMS-7 high resolution instrument. UV-
vis absorption spectra were reported on a Cintra 5 UV-Visible spectrometer. Transition
temperatures and enthalpies were scanned in TA instruments Q1000 DSC, differential
scanning calorimeter with a heating rate of 10.0◦C/min in air and it was calibrated with
indium (156.6◦C, 28.45 J/g). The temperatures were read as the maximum of the endother-
mic peaks. The textures of the mesophases were studied with Olympus BX40 microscope
equipped with a Leitz Laborlux 12 Pols hot stage and PR600 controller.

36
M. K. S. Al-Malki et al.
CH3
COOH
HO
[I]
[IV]
H3C
CH3
(i)
(iii)
CHBr2
[II]n
COOH
RO
[V]
(ii)
Br2HC
CHBr2
(iv)
N
N
CHO
[III]n
NH2
RO
S
[VI]
OHC
CHO
(v)
OR
N
N
S
[VII]n
N
CH
CH
HC
N
N
N
S
N
S
N
N
RO
OR
Scheme 1. Reagents and conditions; (i) MeOH, KOH, appropriate RX, reflux, overnight; (ii) POCl3,
thiosemicarbazide, reflux, 7 hr; (iii) Br2, UV light, 170◦C; (iv) anhydrous morpholine, reflux, 4 hr;
and (v) absolute EtOH, reflux, overnight.
Synthesis and Characterization
The steps of the synthesis of homologous series 1,3,5-tri-[5–4ꢀ-nalkoxyphenyl-1,3,4-
thiadiazole-2-yl-]-trimesilydine [VII]n are shown in the sequence of reactions depicted
in Scheme 1. Where n designate the number of carbon atom in terminal alkoxy group
substituent.
Synthesis of 4-n-alkoxybenzoic acid. 4-n-alkoxybenzoic acid [II]n was obtained fol-
lowing the procedure described in [49].
Synthesis of 5-(4-n-alkoxyphenyl)-2-amino-1,3,4-thiadiazole [III]n. A mixture of
appropriate 4-n-alkoxybenzoic acid (10 mmol) and (0.91 g, 10 mmol) of thiosemicar-
bazide with 5 mL of phosphorus oxychloride was refluxed gently for 5 hr. After cooling

Synthesis and Mesomorphic Properties of New Columnar LC
37
50 mL of water was added, the mixture was then refluxed for 7 hr and filtered, neutralized
with potassium hydroxide. The precipitate was washed with water and recrystallized from
ethanol-water to give titled compound [III]n.
Compound
[III]1
[III]2
[III]3
[III]4
[III]5
[III]6
[III]7
[III]8
Yield%
m.p. ◦C
65
195
65
200
60
188
65
190
60
187
70
180
50
170
45
165
The spectroscopic and elemental characterization of [III]5 example is given: FT-IR
(KBr, cm−1): 3241 (νasy, N–H, NH2), 3101 (νsy, N–H, NH2), 2936–2864 (νC–H, aliphatic), 1609
1
(νC=N, thiadiazole ring), 1018 (νC−O−C, OCH2). HNMR (DMSO, δ in ppm): 7.10–7.70
(d-d, 4H, arom. H), 7.35 (s, 2H, NH2), 4.02 (t, 2H, OCH2), 1.80 (m, 2H, OCH2 CH2), 1.40
(m, 4H, CH2CH2) 0.95 (t, 3H, CH3). Anal, Calcd. for C13H17ON3S; C: 59.32%, H: 6.46%,
N: 15.97%, and S: 12.17%, and found C: 59.24%, H: 6.54%, N: 16.02%, and S: 12.32%.
MS: m/z+1 = 264.
Synthesis of α,α, αꢀ,αꢀ, αꢀꢀ, αꢀꢀ-hexabromomesitylene [V]. To a 100 mL round bottomed
flask containing 23 mL of mesitylene, 15 mL of bromine was added within 2 hr at 155◦C,
another 15 mL of bromine was added also within 6 hr at 170–180◦C. The addition of
bromine was administrated under UV light. The mixture was then refluxed for another 1
hr at 170◦C. After cooling to room temperature the mixture was filtered to give 80% yield
of the titled compound [V], m.p. = 183 ◦C. Anal, Calcd. for C9H6Br6; C: 18.18% and H:
1.01% and found C: 17.71% and H: 1.54%. MS: m/z+1 = 595.
Synthesis of benzene-1,3,5-tricarboxyaldehyde [VI]. A (2.97 g, 5 mmol) of [V] was
dissolved in 22 mL of anhydrous morpholine. The solution was then refluxed for 4 hr by us-
ing water bath, after that the solution was poured into a 25 mL of concentrated hydrochloric
acid with ice, the solution was then filtered, and the precipitate was then dissolved again
in 200 mL boiled water. The solution was neutralized by potassium hydroxide (60% yield
from the titled compound [VI] was obtained by cooling to room temperature), m.p. 154 ◦C.
Anal, Calcd. for C9H6O3; C: 66.67% and H: 3.70% and found C: 67.08% and H: 4.11. MS:
m/z+1 = 163.
Synthesis of 1,3,5-tri-[5(4ꢀ-n-alkoxyphenyl)1,3,4-thiadiazole-2-yl]-trimesilydene
[VII]n. A mixture of appropriate 2-amino-5-(4-n-alkoxyphenyl)-1,3,4-thiadiazole [III]n
(30 mmol) and 1,3,5-triformylbenzene [VI] (1.62 g, 10 mmol) dissolved in 35 mL of abso-
lute ethanol. The mixture was then refluxed for 24 hr with stirring. After cooling to room
temperature the solvent was evaporated, and the precipitate was recrystallized from ethanol.
Compound [VII]1
[VII]2
[VII]3
[VII]4
[VII]5
[VII]6
[VII]7
[VII]8
Yield%
m.p. ◦C
60
195
63
200
50
188
55
190
65
187
60
180
45
170
45
165
The spectroscopic characterization of [VII]5 example is given: FT-IR (KBr, cm−1):
3100 (νC–H aromatic), 2930–2961 (νC–H aliphatic), 1665 (νC = N, imine), 1609 (νC = N
,
1
thiadiazol). HNMR (DMSO, δ in ppm) 8.97 (s, 3H, N = CH), 8.80 (s, 3H, arom. H of
central benzene ring), 7.15–8.15 (d-d, 12H, arom. H), 4.15 (t, 6H, 3 × OCH2), 1.78 (m,
6H, 3 × OCH2 CH2), 1.45 (m, 12H, 6 × CH2), 0.91 (t, 9H, 3 × CH3). MS: m/z+1 = 786.

38
M. K. S. Al-Malki et al.
Table 1. Elemental analysis data for the series [VII]n
Analysis % found (calculated)
Molecular
formula
Molar mass
g/mol
Compound
[VII]1
C
H
N
S
C36H27O3N9S3
C37H29O3N9S3
C38H31O3N9S3
C39H33O3N9S3
C40H35O3N9S3
C41H37O3N9S3
C42H39O3N9S3
C43H41O3N9S3
729
743
757
771
785
799
813
827
59.04
(59.26)
59.68
(59.76)
60.32
(60.24)
59.90
(60.70)
61.10
(61.15)
61.69
(61.58)
61.97
(61.99)
62.36
(62.39)
3,72
(3.70)
3.10
(3.90)
4.21
(4.10)
4.36
(4.28)
4.50
(4.46)
4.68
(4.63)
4.68
(4.80)
5.04
(4.96)
17.58
13.19
(17.28) (13.17)
16.78 12.97
(16.96) (12.92)
16.53 12.81
(16.64) (12.68)
16.35 12.60
(16.34) (12.45)
16.10 12.28
(16.05) (12.23)
15.82 12.04
(15.77) (12.02)
15.58 11.93
(15.50) (11.81)
15.39 11.76
(15.24) (11.61)
[VII]2
[VII]3
[VII]4
[VII]5
[VII]6
[VII]7
[VII]8
Results and Discussion
Synthesis
The 5-(4-n-alkoxyphenyl)-2-amino-1,3,4-thiadiazole [III]n, which is precursors of this
series, were synthesized starting with the reaction of thiosemicarbazide with 4-n-
alkoxybenzoic acid [II]n (n = 1–8) followed by dehydration in POCl3 to form thiadiazole
ring. The synthesis of benzene-1,3,5-tricarboxyaldehyde [VI] was achieved by the reaction
of α,α,αꢀ,αꢀ,αꢀꢀ,αꢀꢀ-hexabromomesitylene [V] with anhydrous morpholine. The1,3,5-tri-
[5(4ꢀ-n-alkoxyphenyl)1,3,4-thiadiazole-2-yl]-trimesilydene [VII]n were obtained by con-
densation of compounds [III]n with the benzene-1,3,5-tricarboxyaldehyde [VI] in absolute
ethanol according to the well-known procedure for the synthesis of Schiff bases.
1
The structures of all products were identified by using FTIR and NMR, and mass
spectrometry as already described in the experimental section. The all resultant data of the
spectra were in accordance with expected values. The purities of compounds were con-
firmed by using an elemental analysis. The elemental analysis of series [VII]n compounds
synthesized above is listed in Table 1. The observed values are in well agreement with
theoretical values indicating structure of respective compounds.
Mesomorphic Properties
The phase transition of compounds of the [VII]n series were studied using polarizing optical
microscopy (POM) and differential scanning calorimetry (DSC). The phase transition
temperatures observed by POM agree well with the corresponding DSC thermograms.

Synthesis and Mesomorphic Properties of New Columnar LC
39
Table 2. Phase transition temperatures (◦C) and enthalpies (kJ/mol, in parentheses) as
determined by DSC, for compounds of series [VII]n
Comp.
[VII]1
Phase behavior
[VII]2
[VII]3
[VII]4
[VII]5
[VII]6
[VII]7
[VII]8
Note: Cr = crystal phase; Colx = undefined columnar phase; I = isotropic phase; all data are
obtained from the second heating cycle.
The phase transitions and thermodynamic data for compounds of the series [VII]n are
summarized in Table 2.
The first three homologous [VII]1–[VII]3 do not reveal any liquid crystalline behav-
ior, but simply changes from the solid crystalline state to the isotropic liquid at 220◦C,
237◦C, and 215◦C for compounds [VII]1, [VII]2, and [VII]3, respectively. Compounds
[VII]4–[VII]8 display enantiotropic mesomorphism. The texture observed by POM on
cooling from the isotropic liquid are consistent with the presence of columnar mesomor-
phism, with fan-shaped typical to columnar phases for compounds [VII]4, [VII]6, and [VII]8
and fan shaped focal conic typical to a columnar hexagonal for compound [VII]5 as shown
in Fig. 1.
The formation of a columnar mesophase was found to be dependent on the number of
methylene units in alkoxy terminal chains attached to the rigid core. The mesophase creation
probably results from two competitive tendencies: stiffening of the molecular core by
dipole-dipole molecular interaction of highly polar methoxy, ethoxy, and propoxy terminal
substituent, which depresses the mesomorphic phases, and elongation of that substituent
promoting these mesophases. The long alkoxy chains probably biased the rotation of
both molecular parts. However, this molecular core is less rigid than that in compounds
[VII]1, [VII]2, and [VII]3, resulting in the formation of columnar phase, which is stable in
narrow temperature range. The mesophase’s stability was found to be poor for the last five
compounds. This suggests that the two strong stiffening of the molecular core depresses
the columnar phase formation. It is worth wide to mention that an increase in the molecular
length with little or no change in the width allow an increase in the anisotropy of the
polarizability for molecules with three thiadiazole rings, which favor molecular interaction
and liquid crystalline properties for these compounds, [VII]4–[VII]8.These results illustrate
the importance of the influence of the number of the methylene unit in terminal alkoxy
chain in the occurrence of columnar order.

40
M. K. S. Al-Malki et al.
Figure 1. Cross-polarizing Optical textures of the columnar mesophase obtained on cooling (Mag-
nification 200×) for compounds of series [VII]n, (a) [VII]4 at 211◦C, (b) [VII]5 at 206◦C, (c) [VII]6
at 198◦C, and (a) [VII]8 at 200◦C.
The effects of the terminal chain length on the transition temperatures and phases
behavior observed in this series are in accordance with those observed for columnar discotic
mesogenes [49–52].
The UV absorption properties of these liquid crystalline molecules have been studied.
The absorption spectra in DMSO solution for these compounds exhibited a distinctive
absorption peak at 310–312 nm which attributed to the π-π∗ transition. These results
showed that these liquid crystalline compounds could emit a blue light in DMSO solution
on photoexcitation.
Conclusions
A new series of discotic liquid crystalline based on 1,3,5-benzenetrisazomethine derivatives
with three pendant 2-amino-5-(4ꢀ-n-alkoxy)phenyl-1,3,4-thiadiazole were designed and
synthesized by varying alkoxy terminal chain length (n = 1–8). The formation of a columnar
mesophase was found to be dependent on the number of methylene unit in alkoxy terminal
chains. The compounds with n ≥ 4, exhibited an anantiotropic columnar phase; however,
compounds with n = 1, 2, and 3 formed a crystalline phase.
References
[1] Chandrasekhs, S., Dashivba, B. K., & Sureshk, K. A. (1977). Pramana, 7, 471–478.
[2] Billard, J., Dubois, J. C., Tinh, N. H., & Zann, A. (1978). Nouv. J. Chim., 2, 535–540.
[3] Destrade, C., Mondon, M. C., & Malthete, J. (1979). J. Phys., Paris, 40, C3–17.
[4] Simpson, C. D., Wu, J., Watson, M. D., & Mu¨llen, K. (2004). J. Mater. Chem., 14, 494–504.

Synthesis and Mesomorphic Properties of New Columnar LC
41
[5] Sergeyev, S., Pisula, W., & Geerts, Y. H. (2007). Chem. Soc. Rev., 36, 1902–1929.
[6] Kato, T., Mizoshita, N., & Kishimoto, K. (2006). Angew. Chem., Int. Ed., 45, 38–68.
[7] Yoshio, M., Mukai, T., Ohno, H., & Kato, T. (2004). J. Am. Chem. Soc., 126, 994–995.
[8] Kato, T., & Toshio, M. (1996). In: Electrochemical Aspects of Ionic Liquids, Ohno, H. (Ed.),
Chapter 25, pp. 307–320, Wiley-Interscience: Hoboken, NJ.
[9] Gin, D. L., Lu, X., Nemade, P. R., Pecinovsky, C. S., Xu, Y., & Zhou, M. (2006). Adv. Funct.
Mater., 16, 865–878.
[10] O’Neill, M., & Kelly, S. M. (2003). Adv. Mater., 15, 1135–1146.
[11] Woltman, S. J., Jay, G. D., & Crawford, G. P. (2007). Nat. Mater., 6, 929–938.
[12] Eich, M., & Wendorff, J. (1987). Macromol. Chem. Rapid Commun., 8, 467.
[13] Chapoy, L. L. (1985). In: Advances in Liquid Crystalline Polymers, Chapoy, L. L. (Ed.), Chapter
21, pp. 311–322, Elsevier: London.
[14] Parikh, V. B., & Menon, S. K. (2008). Mol. Cryst. Liq. Cryst., 482, 71–83.
[15] Pantalone, K., & Seed, A. J. (2002). Liq. Cryst., 29, 945–950.
[16] Zhi-bin, C., Mao, Z., & Jian-rong, G. (2009). Guangxue Jishu, 35(3), 446–450.
[17] Parra, M., Vergara, J., Zuniga, C., Soto, E., Sierra, T., & Serrano, J. L. (2005). Liq. Cryst., 32,
457–462.
[18] Garzon, A., Granadino-Roldan, J. M., Garcia, G., Moral, M., & Fernandez-Gomez, M. (2013).
J. Chem. Phys., 138(15), 154902/1–154902/6.
[19] Seltmann, J., Marini, A., Mennucci, B., Dey, S., Kumar, S., & Lehmann, M. (2011). Chem.
Mater., 23(10), 2630–2636.
[20] Tomma, J. H., Rou’il, I. H., & Al-Dujaili, A. H. (2009). Mol. Cryst. Liq. Cryst., 501, 3–19.
[21] Han, J., Zhang, F. Y., & Wang, J. Y. (2010). Key Eng. Mater., 428–429 (Advances in Liquid
Crystals), 52–56.
[22] McCairn, M. C., & Kreouzis, T. & Turner, M. L. (2010). J. Mater. Chem., 20(10), 1999–2006.
[23] Han, J., Zhang, F. Y., Wang, J. Y., Wang, Y. M., Pang, M. L., & Meng, J. B. (2009). Liq. Cryst.,
36, 825–833.
[24] Han, J., Chang, X. Y., Zhu, L. R., Pang, M. L., Meng, J. B., Chui, S. S. Y., Lai, S. W., & Roy,
V. A. L. (2009). Chem. Asian J., 4(7), 1099–1107.
[25] Han, J., Chang, X., Wang, X., Zhu, L., Pang, M., & Meng, J. (2009). Liq. Cryst., 36(2), 157–163.
[26] Han, J., Chang, X. Y., Zhu, L. R., Wang, Y. M., Meng, J. B., Lai, S. W., & Chui, S. S. Y. (2008).
Liq. Cryst., 35(12), 1379–1394.
[27] Nakashima, S., Sato, M., & Yamaguchi, I. (2008). Polym. Int., 57(1), 39–49.
[28] Parra, M. L., Saavedra, C. G., Hidalgo, P. I., & Elgueta, E. Y. (2008). Liq. Cryst., 35(1), 55–64.
[29] He, C. F., Richards, G. J., Kelly, S. M., Contoret, A. E. A., & O’Neill, M. (2007). Liq. Cryst.,
34(11), 1249–1267.
[30] Seed, A. (2007). Chem. Soc. Rev., 36(12), 2046–2069.
[31] Sato, M., Matsuoka, Y., & Yamaguchi, I. J. (2007). Polym. Sci., Part A: Polym. Chem., 45(14),
2998–3008.
[32] Wang, T., Miao, W., Wu, S., Bing, G., Zhang, X., Qin, Z., Yu, H., Qin, X., & Fang, J. (2011).
Chinese J. Chem., 29(5), 959–967.
[33] Alig, B., Antons, S., Fischer, R., Lui, Norbert, K. A., & Voerste, A. (2011). Patent US No.
20110045104 A1 20110224.
[34] Paspirgelyte, R., Zostautiene, R., Buika, G., Grazulevicius, J. V., Grigalevicius, S., Jankauskas,
V., Chen, C. C., Chung, Y. C., Wang, W. B., & Jou, J. H. (2010). Synthetic Metals, 160(1–2),
162–168.
[35] Bradley, P., Sampson, P., & Seed, A. J. (2005). Liq. Cryst., 14(1), 15–18.
[36] Zhang, Y. D., Jespersen, K. G., Kempe, M., Kornfield, J. A., Barlow, S., Kippelen, B., & Marder,
S. R. (2003). Langmuir, 19, 6534–6536.
[37] Lai, C. K., Ke, Y. C., Su, J. C., Lu, C. S., & Li, W. R. (2000). Liq. Cryst., 29, 915–920.
[38] Wen, C. R., Wang, Y. J., Wang, H. C., Shew, H. S., Lee, G. H., & Lai, C. K. (2005). Chem.
Mater., 17, 1646–1654.
[39] Qu, S., & Li, M. (2007). Tetrahedron, 63, 12429–12436.

42
M. K. S. Al-Malki et al.
[40] He, C., Richards, G., Kelly, S., Contoret, A., & O’Neill, M. (2007). Liq. Cryst., 34, 1249–1267.
[41] Seo, J., Kim, S., Gihm, S., Park, C., & Park, S. (2007). J. Mater. Chem., 17, 5052–5057.
[42] Wang, H., Zhang, F., Bai, B., Zhang, P., Shi, J., Yu, D., Zhao, Y., Wang, Y., & Li, M. (2008).
Liq. Cryst., 35, 905–912.
[43] Kim, B. G., Kim, S., & Park, S. Y. (2001). Tetrahedron Lett., 42, 2697–2699.
[44] Yelamaggad, C. V., Achalkumar, A. S., Rao, D. S. S., & Prasad, S. K. (2009). J. Org. Chem.,
74, 3168–3171.
[45] Kim, B. G., Kim, S., & Park, S. Y. (2001). Mol. Cryst. Liq. Cryst., 370, 391–394.
[46] Barbera, J., Godoy, M. A., Hidalgo, P. I., Parra, M. L., Ulloa, J. A., & Vergara, J. M. (2011).
Liq. Crys., 38, 679–688.
[47] Choi, E. J., Xu, F., Son, J. H., & Zin, W. C. (2011). Mol. Cryst. Liq. Cryst., 551, 60–68.
[48] Parra, M. L., Elgueta, E. Y., Ulloa, J. A., Vergara, J. M., & Sanchez, A. I. (2012). Liq. Cryst.,
39, 917–925.
[49] Boden, N., Bomer, R. C., Bushby, R. J., Cammidge, A. N., & Jesklason, M. V. (1993). Liq.
Cryst., 15, 851–858.
[50] Chang, J. Y., Baik, J. H., Lee, C. B., & Han, M. J. (1997). J. Am. Chem. Soc., 119, 3197–3198.
[51] Ebert, M., Jungbauer, D. A., Kleppinger, R., Wendorff, J. H., Kohne, B., & Praefcke, K. (1989).
Liq. Cryst., 4, 53–67.
[52] Thaker, B. T., Patel, P., Vansadia, A. D., & Patel, H. G. (2007). Mol. Cryst. Liq. Cryst., 2007,
466, 13–22.