Synthesis and mesomorphic properties of Schiff base esters possessing terminal chloro substituent Sie Tiong Ha a, * , Lay Khoon Ong b , Siew Ling Lee c , Hong Cheu Lin d , Yip Foo Win a , Siew Teng Ong a a Department of Chemical Science, Faculty of Science, Universiti Tunku Abdul Rahman, Jln Universiti, Bandar Barat, 31900 Kampar, Perak, Malaysia b Department of Science, Faculty of Engineering & Science, Universiti Tunku Abdul Rahman, Jln Genting Klang, Setapak, 53300 Kuala Lumpur, Malaysia c Ibnu Sina Institute for Fundamental Science Studies, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia d Department of Materials Science & Engineering, National Chiao Tung University, Hsinchu 300, Taiwan, China Received 25 November 2009 Abstract A homologous series of Schiff base esters, 4-chlorobenzylidene-4 0 -n-alkanoyloxyanilines, containing even number of carbons at the end groups of the molecules (C nÀ1 H 2nÀ1 COO–, n = 4, 6, 8, 10, 12, 14, 16) were synthesized. The mesomorphic properties were investigated by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). It was found that the end groups of the molecules had an effect on the mesomorphic properties. n-Butanoyloxy was found non-mesogenic, whilst n-hexanoyloxy exhibited monotropic smectic phase. The higher members in this homologous series were enantiotropic smectogens. # 2010 Sie Tiong Ha. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Schiff base esters; Smectic A; Smectic B; Liquid crystal The discovery of thermotropic liquid crystal 4-methoxybenzylidene-4 0 -butylaniline and the application of its room temperature nematic phase in displays sparked a renewed interest liquid crystals and in research to establish structure– liquid crystal property relationships [1,2]. The understanding of structure–property relationships is elemental to selecting molecular modifications for the synthesis of new mesogens with desirable properties and future applications [3]. In the previous studies, it was revealed that ester and Schiff base linking units are the useful structural components for generating mesomorphism in two and three aromatic rings thermotropic liquid crystals [4–7]. Therefore, a continuing effort has been carried out which focused on the synthesis and characterization of a new series of Schiff base esters possessing terminal halogen substituent, 4-chlorobenzylidene-4 0 -n-alkanoyloxyanilines. The synthesis of the target molecules is shown in Scheme 1, where 4-chlorobenzaldehyde was coupled with 4-aminophenol by heating under reflux for about 3 h in ethanol solution. Then, the Schiff base intermediate was subjected to esterification with www.elsevier.com/locate/cclet Available online at www.sciencedirect.com Chinese Chemical Letters 21 (2010) 637–640 * Corresponding author. E-mail addresses: hast_utar@yahoo.com, hast@utar.edu.my (S.T. Ha). 1001-8417/$ – see front matter # 2010 Sie Tiong Ha. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2010.01.023