LIQUID-CRYSTALS OF 4-OCTYLOXY-N-(BENZYLIDENE)ANILINE DERIVATIVES BEARING TRIFLUOROMETHYL OR TRIFLUOROMETHOXY END-GROUPS

Seven new derivatives of 4-octyloxy-N-(4-substituted benzylidene) anil ine have been synthesized. 4-Trifluoromethyl and 4-trifluoromethoxy de rivatives exhibit stable smectic B and A phases, respectively, while b oth the 4-methyl and 4-methoxy derivatives have monotropic nematic pha ses. Fundamental liquid crystalline properties such as entropies of th e phase transitions, microscopic textures, smectic layer spacings, ori entational order parameters, and molecular dipole moments were determi ned. It has been revealed that moderately polar nature of these mesoge ns act to stabilizing monolayer smectic states. The smectic A phase of 4-trifluoromethoxy derivative exhibit very high orientational order. None of the disubstituted compounds, 3,5-bis(trifluoromethyl), 3,5-dim ethyl, and 3,5-dimethoxy derivatives were mesogenic. The effect of ter minal trifluoromethylation on the liquid crystalline properties is dis cussed.