Bent-shaped mesogenic oxadiazole and thiadiazole derivatives from rod-shaped mesogenic hydrazide containing polar chloro group

Rod-shaped mesogenic hydrazide (series I) derivatives have been synthesised by the Schotten-Baumann reaction of 4-chlorobenzhydrazide with 4-n-alkoxybenzoyl chloride using pyridine as a solvent. Rod-shaped mesogenic hydrazide (series I) have been cyclised to bent-shaped mesogenic oxadiazole (series II) and thiadiazole (series III) derivatives using POCl3 and P2S5, respectively. The synthesised compounds are characterised by a combination of elemental analysis and standard spectroscopic methods. All the compounds of present series I–III exhibit smectic A mesophase. The mesomorphic properties of the present series I–III are compared with each other and with the other structurally related mesogenic homologous series to evaluate the effect of bent-shape and different heterocyclic moiety on mesomorphism.