The effect of chain length in terminal groups on the mesomorphic behavior of novel (-)-menthol-based chiral liquid crystal compounds with a blue phase

In this study, two series of novel chiral liquid crystal compounds derived from (-)-menthol with different lengths of alkyl or alkoxy as terminal groups were successfully synthesized. Their chemical structure and liquid crystal properties were investigated by various experimental techniques. Series I, except for compound If, exhibits monotropic properties and the whole series II shows enantiotropic mesogenic properties. Both series I and series II display a platelet texture of a BP and a focal conic texture of an N-star phase upon cooling. In addition, series II displays an iridescent oily streak texture along with selective reflection upon heating. The selective reflection wavelengths of series II shift to a shorter wavelength region with increasing temperature in the N-star phase. For both series I and series II, a pronounced odd-even effect on the clearing temperature is observed when the parity of the terminal chain is varied. Series I with an odd number of terminal chains and series II with an even number have better order.