Synthesis and Anisotropic Properties of Azo-Bridged Benzothiazole-Phenyl Esters

Abstract

A new series of benzothiazole-phenyl esters intersected by azo N˭N has been isolated and their structures were characterized. These compounds exhibit enantiotropic nematic phase. The transition temperatures and the enthalpy values associated with these derivatives were found to be dictated by the variation of the lengths of the flexible alkoxyl chains (OOCC _n H_2n+1 where n adopts even numbers from 5 to 17). A noteworthy characteristic of this series is the clearing temperatures, which decrease upon lengthening of the alkoxyl chains from n = 5 to n = 17. A descending stability associated with the nematic phase range was also observed when the carbon number in the alkyl group increased. A comparative study between the title compounds and 6-ethoxy-2-(4-alkanoxybenzylidenamino)benzothiazole shows that the present compounds favor the formation of N phase while the previously reported analogs, which contain C˭N instead of N˭N, exhibited enantiotropic N and SmC phases.

Keywords:

• Azo linkage
• benzothiazoles
• enantiotropy
• nematic phase
• phenyl esters

Acknowledgment

The authors would like to thank Universiti Sains Malaysia for funding the project through FRGS Grant (Account No. 203/PKIMIA/6711192).