Synthesis and mesomorphic properties of 4-alkylamino-4'-substituted diphenyldiacetylenes

Various substituted aminodiphenyldiacetylenes of the type with X = C₃H₇, C₅H₁₁, F or NO₂ and R, R' = H, CH₃-C₆H₁₃ were synthesized and their mesomorphic properties determined. Semi-empirical and ab initio quantum chemical calculations using AM1, 421G and 631G* suggested that the amino group would increase the dielectric anisotropy and optical birefringence as compared to the alkyl chain. Mesomorphic properties were found to be poor with the maximum nematic phase range being 44.8°C and many of the compounds having no nematic phase. Both melting temperatures and enthalpies for those having nematic phases were too high to form good eutectic mixtures.