TGB_A and TGB_C phases in some chiral tolan derivatives

Three chiral compounds (n=10, 11, 12) belonging to the optically active series : 3-fluoro-4-[(R) or (S)-1-methylheptyloxy]-4'-(4$''$-alkoxy-2$''$, 3$''$-difluorobenzoyloxy) tolans (nF2BTFO1M7) have been synthesized. The helical SA* phase or TGBA phase is found in the decyloxy derivative. The most interesting compound is obtained with n=11. It displays, for the first time, two TGB phases (TGBA and TGBC phases). The nature of these helical smectic phases is confirmed by different studies : optical observation, DSC, contact method, mixtures, X-ray diffraction and helical pitch measurements. the electrooptical properties of the SC* phase have also been studied.