%0 Journal Article
%T Synthesis and Mesomorphic Properties of New Fluorinated Schiff Base Liquid Crystals
%A Sie-Tiong Ha
%A Teck-Leong Lee
%J ISRN Materials Science
%D 2014
%R 10.1155/2014/904657
%X Two new compounds, 4-alkanoyloxybenzylidene- -fluoroaniline and 4-fluorobenzylidene- -n-alkanoyloxyaniline comprising a terminal fluorosubstituent were studied. The fluoro substituent contributes to the molecular polarizability, thus affecting intermolecular interactions and hence resulting in smectic mesomorphism. The mesomorphic properties were studied using differential scanning calorimetry and polarizing optical microscopy techniques. The mesomorphic properties of compounds studied are strongly dependent on the orientation of the imine (CH=N) linkage. The former Schiff base exhibited smectic A phase whereas the latter compound did not display any mesophase. Reversed imine linkage has caused depression of mesomorphic property in the compound studied (4-fluorobenzylidene- -n-alkanoyloxyaniline). The mesomorphic properties of the present compounds were compared with other structurally related series to establish the chemical structure-mesomorphic property relationship. 1. Introduction Liquid crystals (LCs) have many practical applications in scientific and technological areas, in particular as display devices, OLEDs, anisotropic networks, photoconductors, and semiconductor materials [1¨C3]. Strong demand of new LCs for applications has led to the synthesis of wide range of mesogens, in particular, thermotropic liquid crystals [4, 5]. Most thermotropic liquid crystals belonged to the calamitic molecules which have a rigid core that consisted of two or more phenyl rings and one or more flexible terminal alkyl chains. Schiff base is one of the most well-known linking groups used in connecting the rigid core groups. Although it provides a stepped core structure, it maintains molecular linearity, therefore providing better stability and inducing formation of mesophase [6, 7]. Numerous works have been reported in this area ever since the discovery of MBBA which exhibited room temperature nematic phase [8]. Recently, ester type of Schiff bases has received considerable attentions owing to their interesting properties and substantial temperature range [9¨C18]. Structure-property relationship is essential knowledge for molecular modifications of the synthesis of new mesogens with targeted properties and future practical applications [6]. Typical terminal substituents exhibiting LC properties are those with electronegative atoms, such as halogens. Halogens are polar substituents possessing strong dipole moments, thus having the ability to promote mesomorphic properties [19¨C21]. The increased dipole moment enhances the stability of the lattice and melting
%U http://www.hindawi.com/journals/isrn.materials.science/2014/904657/