New Mesogenic Schiff Base Esters with Polar Chloro Substituent: Synthesis, Thermotropic Properties and X-Ray Diffraction Studies
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Copyright: © 2020 Sie-Tiong Ha, Lay-Khoon Ong, Yasodha Sivasothy, Guan-Yeow Yeap, Peng-Lim Boey and Hong-Cheu Lin. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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.
- liquid crystal
- smectic A
- smectic B
- X-ray diffraction