Liquid crystalline dimers containing a cholesteryl group: Chiral smectic phases, and re-entrant TGBA* phase

A new series of liquid crystalline dimers containing a cholesteryl group were synthesized, exhibiting multiple mesophases including chiral smectic phases (SmX*, SmC* and SmA*), twist grain boundary phases (TGBA* and TGBC*), and chiral nematic phase (N*). Re-entrant phenomenon occurs, which is rarely reported for pure matters of dimeric liquid crystals. The chemical structure and liquid crystal properties of the dimers were characterized by FTIR, 1 H NMR, DSC, POM and XRD. It was in evidence that the length and the parity of the spacer and the length of the terminal tail were the decisive factors of the mesophase behaviours.