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

A series of azo-bridged benzothiazole-phenyl ethers 4-((6-ethoxybenzothiazol-2-yl)diazenyl)bromoalkoxybenzene in which an exocyclic NN 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 = 912 also behave as smectogens.