Under pressure studies of TGBA and TGBC phases on pure compounds

Abstract High pressure experiments have been performed on three homologous (n=9 to 11) of the 3-fluoro-4-[(R) or (S)-methylheptyloxy]-4′-(4″-alkoxy-2″,3″-difluorobenzoyloxy) tolans series which exhibit the TGBA and TGBc phases. The transitions were detected by thermobarometric analysis. For n=9, the TGB4 temperature stability domain versus pressure first increases, then rises to a maximum and finally disappears in the SA-TGBA TGBA -N* multicritical point. An induced SA phase appears under pressure for n = 10 leading to the observation of SC*-SA-TGBA multicritical point. For the first time, a (P-T) phase diagram exhibiting simultaneously and clearly the both domains TGBA and TGBC phases is obtained for n=11. These results confirm the existence of singular points previously predicted by the Renn and Lubensky theory.