Download Synthesis and characterization of azo benzothiazole

Materials Chemistry and Physics xxx (2013) 1e10
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Materials Chemistry and Physics
journal homepage: www.elsevier.com/locate/matchemphys
Synthesis and characterization of azo benzothiazole chromophore based liquid
crystal macromers: Effects of substituents on benzothiazole ring and terminal
group on mesomorphic, thermal and optical properties
Md. Rabiul Karim a, Md. Rezaul Karim Sheikh a, *, Noordini M. Salleh a, Rosiyah Yahya a, Aziz Hassan a,
Md. Asadul Hoque b, c
a
b
c
Department of Chemistry, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia
Department of Materials Science and Engineering, University of Rajshahi, Rajshahi 6205, Bangladesh
Chemical Resources Laboratory, Tokyo Institute of Technology, 4259-R1-25, Nagatsuta-Cho, Midori-Ku, Yokohama 226-8503, Japan
h i g h l i g h t s
Benzothiazole based liquid crystalline macromers were synthesized and characterized.
Sixth position substituents of benzothiazole influenced the mesophase properties.
Terminal methacrylate group also influenced the mesophase formation.
The absorption maxima were red shifted by the electron pushing groups.
OCH3 at 6th position of benzothiazole exhibited highest fluorescence emission.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 July 2012
Received in revised form
19 March 2013
Accepted 9 April 2013
A series of azo benzothiazole chromophore based liquid crystalline compounds having different substituents at the sixth position on benzothiazole moiety with methacrylate terminal group were synthesized and characterized by FTIR, 1H and 13C NMR. TGA investigations showed synthesized compounds
were thermally stable. POM and DSC studies revealed that all the compounds showed liquid crystal
behaviors. SAXS analysis exposed that all the investigated compounds exhibited lamellar structure.
Compound with H at the sixth position on the benzothiazole ring revealed only smectic liquid crystal
phase whereas compounds with CH3, OCH3 and OC2H5 groups showed both nematic and smectic liquid
crystal phases. The formation of mesophases as well as temperature ranges of mesophases was greatly
influenced by the sixth position electron pushing substituent on benzothiazole ring as well as terminal
methacrylate group. The absorption maxima (lmax) of UVevis spectra were bathochromically shifted
with the replacement of sixth position hydrogen atom by the electron donating groups on benzothiazole
chromophore. Macromer with OCH3 substituent exhibited highest fluorescence emission than other
compounds.
Ó 2013 Elsevier B.V. All rights reserved.
Keywords:
Liquid crystals
Chemical synthesis
Optical microscopy
Optical properties
1. Introduction
Azobenzene based liquid crystalline (LC) materials, either low
molecular weight or polymeric in nature, are fascinating and
promising class of compounds due to their unique electrical, optical
and mechanical properties. The photochemical properties of
azo compounds make them potential in variety of optical and optoelectronic applications such as nonlinear optical devices [1e3],
* Corresponding author. Tel.: þ60 3 79674067; fax: þ60 3 79674193.
E-mail addresses: [email protected], [email protected] (Md.R.K. Sheikh).
optical data storage [4,5], optical switching devices [6e9], LC
display devices [10e12] and so forth.
Many mesogenic compounds comprising single ring heterocyclic moieties have been synthesized and their properties also
reported in the literature [13e22]. The introduction of heterocyclics
in mesogens of calamatic molecules has great influence on mesophase formation, the phase transition temperatures, dielectric
constants and other properties of the mesogens [23]. Recently, LC
materials with heterocyclic fused ring system have extensively
been studied because of their important properties as photoconductive materials, e.g., benzothiazole based LC compounds [24].
Moreover, benzothiazole fused ring system shows good hole-
0254-0584/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.matchemphys.2013.04.003
Please cite this article in press as: Md.R. Karim, et al., Synthesis and characterization of azo benzothiazole chromophore based liquid crystal
macromers: Effects of substituents on benzothiazole ring and terminal group on mesomorphic, thermal and optical properties, Materials
Chemistry and Physics (2013), http://dx.doi.org/10.1016/j.matchemphys.2013.04.003