Chinese Chemical Letters
Original article
New mesomorphic benzothiazol derivatives: Synthesis and
characterization
d
e
Teck-Ming Koh a, Sie-Tiong Ha b,c, , Guan-Yeow Yeap , Hong-Cheu Lin
*
a Faculty of Engineering & Science, Universiti Tunku Abdul Rahman, Jln Genting Klang, Setapak, Kuala Lumpur 53300, Malaysia
b Faculty of Science, Universiti Tunku Abdul Rahman, Jln Universiti, Bandar Barat, Kampar 31900, Malaysia
c Centre for Biodiversity Research, Universiti Tunku Abdul Rahman, Jln Universiti, Bandar Barat, Kampar 31900, Malaysia
d Liquid Crystal Research Laboratory, School of Chemical Sciences, Universiti Sains Malaysia, Minden 11800, Malaysia
e Department of Materials Science & Engineering, National Chiao Tung University, Hsinchu 300, Taiwan, China
A R T I C L E I N F O
A B S T R A C T
Article history:
In this paper, the synthesis of new mesomorphic benzothiazolyl derivatives, 6-ethoxy-2-[4-(4-
alkyloxybenzoyloxy)benzylidenamino]benzothiazoles, is presented. The structures of the title
compounds were elucidated using spectroscopic techniques, such as FT-IR, NMR (1H and 13C),
elemental analysis and EI-MS. The mesomorphic behaviours of these compounds were determined by
differential scanning calorimetric and polarizing optical microscopic techniques. Compounds exhibited
nematic and tilted smectic phases upon heating from crystal phase. An obvious odd-even effect was
observed in this homologous series.
Received 12 April 2013
Received in revised form 23 May 2013
Accepted 29 May 2013
Available online 2 July 2013
Keywords:
Benzothiazole
Nematic
ß 2013 Sie-Tiong Ha. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights
reserved.
Smectic C
Mesomorphic
1. Introduction
of the heteroatoms, sulfur and nitrogen [14]. In this paper, we
report another new homologous series of benzothiazole liquid
The electronic conducting behaviours of liquid crystals (LCs)
have received tremendous attention since the discovery of high
hole mobility in the hexagonal columnar phase of hexapenthyloxy-
triphenylene [1–5]. Recently, calamitic LCs became another
potential material for applications in electronic devices due to
the presence of some ordered mesophases, such as SmA, SmC, SmB
and SmE. The two-dimensional (2D) arrangement (layers) in
smectics is more tolerant with regard to defects than the one-
dimensional (1D) ordered discotic columns, thus resulting in an
improved performance [6]. The electronic conducting behaviour of
calamitic LCs was first examined in the SmA phase of 2-
phenylbenzothiazole derivatives. Existence of a layer(ed) structure
crystals (Scheme 1). Three core units (one benzothiazole and two
phenyl rings) were connected via a Schiff base and ester linkers
which can increase the molecular broadness and anisotropy.
2. Experimental
The synthetic protocol towards (producing/creating) the title
compounds, 6-ethoxy-2-[4-(4-alkyloxybenzoyloxy)benzylidena-
mino]-benzothiazoles (C2H5O-nBSPEP, where n = 7, 8, 9, 10, 12,
14) is illustrated in Scheme 1. 2-Amino-6-ethoxybenzothiazole
was condensed with 4-hydroxybenzaldehyde upon refluxing in
ethanol for 3 h to yield intermediate A [11]. Etherification of ethyl-
4-hydroxybenzoate in acetone with the appropriate 1-bromoalk-
ane and acidification using concentrated HCl produced intermedi-
ate B [15]. Intermediates A and B were then subjected to Steglich
esterification with the appropriate fatty acid in the presence of DCC
and DMAP according to previously reported procedures [16] to
yield title compounds C2H5O-nBSPEP. All the crude products were
purified by repeated recrystallization using ethanol until constant
melting points were obtained. The yields of the final products were
between 29% and 55% (Scheme 1). Structural elucidation of the title
compounds was carried out via elemental analysis, FT-IR, NMR,
and EI-MS spectroscopic techniques [17].
in all smectic LCs induces
p–p stacking interactions which can
facilitate the hopping of charge carrier mobility [7–9].
In our previous studies, we successfully synthesized and
isolated a series of homologues of smectic LCs containing the
benzothiazole moiety [10–13]. Incorporation of benzothiazole ring
into calamitic LCs, as the mesogenic core, enabled them to easily
exhibit mesophase transitions due to the more polarizable nature
* Corresponding author at: Faculty of Science, Universiti Tunku Abdul Rahman,
Jln Universiti, Bandar Barat, Kampar 31900, Malaysia.
1001-8417/$ – see front matter ß 2013 Sie-Tiong Ha. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.