1ST OBSERVATION OF A S-ASTERISK-C-S(A)-TGB(A) MULTICRITICAL POINT IN A PURE COMPOUND

High pressure experiments have been performed by thermobarometric anal ysis on two homologous (n = 10 and 11) of the [3-fluoro-4((R) or (S)-m ethylheptyloxy) 4'-(4''-alkoxy-3''-fluorobenzoyloxy) tolans series, wh ich both exhibit the TGAMMAB(A) phase. The character (first or/and sec ond order) of the transitions involving the TGB(A) Phase are determine d from thermobarograms. The pressure-temperature phase diagrams show t hat the TGB(A) phase is stabilized under high pressure for the two com pounds. For n = 11 an induced S(A) phase is observed under high pressu res leading to the first experimental observation, on pressure-tempera ture phase diagram of pure compounds, of a S(C)-S(A)-TGB(A) multicrit ical point, previously predicted by the Renn-Lubensky theory.