Nematic-Isotropic Transition Temperature and Dipole-Dipole Interaction. 4-(4-X-Substituted Phenyliminomethyl)phenyl 4-Y-Substituted Benzoates and 4-X-Substituted Phenyl 4-(4-Y-Substituted Phenyliminomethyl) benzoates

摘要

Nematic-isotropic transition temperature was determined for 4-(4-X-phenyliminomethyl)phenyl 4-Y-benzoates and 4-X- phenyl 4-(4-Y-phenyliminomethyl)benzoates, where X and Y are CN, CH_3O,NO_2, Cl, Br, N(CH_3)_2, CH_3, F, or CF_3 groups. The transition temperature in the absence of the dipole-dipole interaction was estimated by extending Van der Veen's approximation. While a large positive deviation is found for the CH_3O-NO_2 derivatives, indicating the signify-cant contribution of dipole-dipole interaction to the nematic thermal stability, no deviation in the CH_3O-CN derivatives suggests the anti-parallel molecular association in the mesophase.