Effect of molecular structure on the phase behavior of some liquid crystalline compounds and their mixtures: X. Unsymmetrical 1,4-phenylene-bis-(4-substituted benzoates)

Four series of unsymmetrical 1,4-phenylene-bis-(4-substituted benzoates) were prepared in which one substituent is a terminal alkoxy group with a number of carbon atoms kept constant (at n=6, 8, 14, and 16) while the other substituent (X) alternatively changed from CH3O, CH3, Cl, NO2, CN, and CnH2n+1O. Compounds prepared were characterized by infrared spectroscopy and their mesophase stabilities investigated by differential scanning calorimeter (DSC) and polarized-light microscope. The results were discussed in terms of mesomeric and polarizability effects. In all the four series, the mesophase–isotropic transition temperatures (Tc) were successfully related to the polarizability anisotropy of bonds to the small compact substituent, X.