Three chiral tolane series with twist grain boundary smectic A and C mesophases

The syntheses of three chiral tolane series are described. The mesomorphic properties together with transition temperatures and enthalpies, ferroelectric properties, helical pitch measurements, phase diagrams and X-ray diffraction (XRD) data are given. Several compounds display twist grain boundary smectic A (TGB(A)) and/or TGB(C) phases. The ortho position of the fluoro-substituent with regard to the chiral chain was found to favour the formation of these new helical phases. The variations in helicity are shown to be specific for several phases and transitions. Edge dislocations of the twisted array of smectic blocks can be observed visually. The first example of a commensurate TGB(C) phase has been found by XRD. These last results prove the Renn-Lubensky (RL) model of the TGB phases. Most critical points of the RL phase diagram are identified.