The effect of substituents on the liquid crystalline behavior of new H-shaped dimesogenic compounds

A series of new dimesogenic compounds were prepared and their thermotropic and liquid crystalline properties were studied by differential scanning calorimetry and on a hot-stage of a polarizing microscope. These compounds, 1,10-bis(2,5-bis(4-substitutedphenoxycarbonyl)phenoxy)decanes, consist of two bis(ρ-substitutedphenoxy)terephthalate units interconnected through a oxydecamethyleneoxy spacer on the central terephthaloyl units resulting in the structure of 'H-shaped' dimeric twin compounds. The terminal substituent groups were changed; X=F, -H, -I, -Cl, -Br, -NO2, -CF3, -OC4H9, -CN, and -C6H5. The compounds with X=OC4H9, -CN and -C6H-5 were monotropically nematic. In contrast, the compounds with X=-F, -H, -I, -Cl, -Br, -NO2 and -CF3 were non-liquid crystals. The nematic group efficiency of these compounds was in the order of -C6H5>-CN>-OC4H9