Synthesis and liquid crystalline properties of new H-shaped twin compounds: a series of 1,6-bis[2,5-bis(4-alkoxyphenoxycarbonyl)phenoxy]hexanes

A new series of laterally linked novel twin mesogenic compounds were synthe sized and their liquid crystalline properties studied by differential scann ing calorimetry, polarizing microscopy and X-ray analysis. The compounds, 1 ,6-bis[(2,5-bis(4-alkoxy)phenoxycarbonyl)phenoxy]- hexanes, consisted of tw o identical mesogenic structures of bis(alkoxyphenoxy)terephthalate linked laterally on the terephthalate centre through a 1,6-dioxyhexane spacer. The length of the terminal alkoxy groups was varied from the ethoxy to the hep tyloxy group; the dodecyloxy group was also included in the present study. It was found that the compounds carrying the ethoxy to hexyloxy groups are monotropically nematic whereas that carrying the heptyloxy groups is enanti otropically nematic. Only the compound with the longest dodecyloxy terminal s forms the smectic A phase enantiotropically.