New Mesogenic Schiff Base Esters with Polar Chloro Substituent: Synthesis, Thermotropic Properties and X-Ray Diffraction Studies

Ha Ha

doi:10.3844/ajassp.2010.214.220

Abstract

Problem statement: Many studies have been conducted on the Schiff base’s alkyl and alkyloxy possessing terminal halogen substituent. However, the thermotropic properties of Schiff base’s ester (or alkanoyloxy) with chloro terminal group remained unstudied. Approach: Synthesis a series of new Schiff base ester possessing polar chloro group and investigate its mesomorphic properties. The title compounds were prepared via condensation and esterification reactions. The molecular structures were confirmed using spectroscopic techniques. All the members are differed by the length of alkanoyloxy chain, Cn-1H2n-1COO, where n = 2-8, 10, 12, 14, 16 and 18. The mesomorphic properties were studied using differential scanning calorimetry, polarizing optical microscopy and temperature-dependent X-ray diffractometry. Results: Whilst short members (n = 2-5) were not mesogenic compounds, n-hexanoyloxy and n-heptanoyloxy derivatives exhibited monotropic SmA and SmB phases. Enantiotropic smectogenic A and monotropic smectogenic B were observed in n-octanoyloxy to n-hexadecanoyloxy derivatives. Highest member of the series, n-octadecanoyloxy derivatives exhibited monotropic SmA phase. Conclusion: The ester linkage and polar terminal group in the present series are essential for the formation of liquid crystal phase in Schiff bases.

Highlights

With development of liquid crystal science and technology, more mesogens have been prepared and studied
A lot of studies have been conducted on the Schiff base possessing ester chain or called Schiff base esters owing to their interesting properties and considerable temperature range (Ha et al, 2009a; 2009b; Yeap et al, 2004; 2006a; 2006b; 2006c)
Synchrotron powder X-Ray Diffraction (XRD) measurements were performed at beamline BL17A where the X-ray wavelength used was 1.32633 Å

Summary

Introduction

With development of liquid crystal science and technology, more mesogens have been prepared and studied. Thermotropic liquid crystal is one of type of mesogens currently extensively studied (Yuksel et al, 2007; Zhang et al, 2005). Known as imine (CH=N), is a linking group used to connect between core groups. It provides a stepped core structure but still maintained the molecular linearity in order to exhibit higher stability and form mesophases (Collings and Hird, 1997; Singh and Dunmur, 2002). Extensive studies on Schiff base core system had been conducted ever since discovery of MBBA showing nematic phase at room temperature (Kelker and Scheurle, 1969). A lot of studies have been conducted on the Schiff base possessing ester chain or called Schiff base esters owing to their interesting properties and considerable temperature range (Ha et al, 2009a; 2009b; Yeap et al, 2004; 2006a; 2006b; 2006c)

Methods

Results

Discussion

Conclusion