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

Abstract

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, CH₃O, NO₂, Cl, Br, N(CH₃)₂, CH₃, F, or CF₃ 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 CH₃O-NO₂ and CH₃−NO₂ derivatives, indicating the significant contribution of dipole-dipole interaction to the nematic thermal stability, no deviation in the CH₃O-CN derivatives suggests the anti-parallel molecular association in the mesophase.

Key Words:

• nematic
• terminal groups
• dipole-dipole interaction
• anti-parallel dimerization