Helical smectic A* phase (TGB_aphase) in some tolan series

Abstract

Abstract A helical smectic A* phase between the isotropic liquid and the ferroelectric smectic C* phase is found in three new series with very long alkoxy chains. The materials belong to the optically active series: (R) and (S) 1-methylheptyl 4′-(4″-alkoxybenzoyloxy)tolan-4-carboxylates, 4′-(4″-alkoxy-3″-fluorobenzoyloxy)tolan-4-carboxylates, 4′-(4″-alkoxy-2′,3″-difluorobenzoyloxy)tolan-4-carboxylates. This new phase has two typical textures: filament texture when the helix pitch is large and cholesteric texture (Grandjean texture) with a short pitch.