Synthesis and Terminal Chain Effect on the Phase Transition Behavior of Azo-Bridged Benzothiazole-Phenyl Ethers

Abstract

A series of azo-bridged benzothiazole-phenyl ethers 4-((6-ethoxybenzothiazol-2-yl)diazenyl)bromoalkoxybenzene in which an exocyclic N˭N group is situated between an ethoxy-substituted benzothiazole and a bromoalkoxyphenyl have been synthesized and characterized. The phase transition behavior of these compounds have been correlated against the variation of the flexible alkyl chain with n methylene units (CH₂), ranging from 5 to 12. The thermal stability as reflected by the transition temperature range of the present homologues is found to be strongly dependent on the length of the CH₂ units. All the members of this series exhibit enantiotropic nematic phases. However, upon further cooling, the compounds with n = 9–12 also behave as smectogens.

Keywords:

• Azo-bridged
• benzothiazole
• ethers
• mesogenic
• nematic
• smectic

Acknowledgment

The main author (G-Y. Yeap) would like to thank Universiti Sains Malaysia for funding the project through an FRGS (Fundamental Research Grant Scheme) grant (account no. 203/PKIMIA/6711192).