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

Author(s): Sie-Tiong Ha | Lay-Khoon Ong | Yasodha Sivasothy | Guan-Yeow Yeap | Peng-Lim Boey | Hong-Cheu Lin

Journal: American Journal of Applied Sciences
ISSN 1546-9239

Volume: 7;
Issue: 2;
Start page: 214;
Date: 2010;
Original page

Keywords: Azomethine | liquid crystal | smectic A | smectic B | X-ray diffraction

Problem statement: Many studies have been conducted on the Schiff bases alkyl and alkyloxy possessing terminal halogen substituent. However, the thermotropic properties of Schiff bases 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.
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