Unveiling the influence of inner spacer length of the non-linear S-shaped chiral oligomers on liquid crystalline phase

A series of S-shaped liquid crystal oligomers consisting of biphenylene, catechol and cholesterol moieties have been synthesized and characterized. The members in this series differ by the length of inner spacers -(CH2)n- where n are varied from 4 to 9 whereas the outer spacer of undecanoate chain is remained intact. The texture and phase transition temperatures with associated enthalpy changes are recorded. Increase in the number of carbon atom at the inner spacer affects the stability of liquid crystalline phase. The homologues with shorter inner spacers n = 4 and 5 exhibit monotropic N* whilst the analogue with medium spacer n = 6 exhibits monotropic N* and SmC* phase. However, the oligomers with longer spacers n = 7, 8 and 9 exhibit enantiotropic N* and SmC* phase. The I-N* transition temperatures were found to depend on the parity of the inner spacers. An X-ray diffraction study reveals that the S-shaped oligomers exist as a monolayer chiral smectic C phase.