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.