Occurrence of the B7 mesophase in two homologous series of seven-ring achiral compounds composed of banana-shaped molecules

The synthesis and mesomorphic behaviour of twenty compounds belonging to two new series of seven-ring esters derived from 2-cyanoresorcinol are reported. Many homologues of both series exhibit the B₇ mesophase. In addition, some of the lower homologues exhibit a mesophase which shows textural features similar to that of the two-dimensional B₁ phase. The characterization of the mesophases has been carried out using polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction, miscibility studies and electro-optical investigations. The first example of a plot of the B₇-isotropic phase transition temperature as a function of the alkyl chain length is also reported.