The Synthesis of Several Lateral Difluoro-substituted 4,4″-Dialkyl- and 4,4″-Alkoxyalkyl-Terphenyls and a Rationalisation of the Effect of Such Substitution on Mesophase Type and Transition Temperatures

In recent years we have prepared a large number of mono-fluoro- and ortho-difluoro-substituted 4,4″-dialkyl- and 4,4″-alkoxyalkyl-terphenyls. The synthesis and transition temperatures of a variety of related difluoro compounds is presented here so that it is now possible to identify (i) broadening of the molecule, (ii) twisting about an inter-annular bond, and (iii) the presence of an ‘inner’ (2-, 2′-, 3′- or 2″-substituent) or an ‘outer’ (3- or 3″-substituent) fluorine, as being the major factors which influence the type and the thermal stability of the mesophases obtained.