关键词: 薄荷基, 液晶单体, 手性近晶C相, 胆甾相, 蓝相

One new chiral non-mesogenic monomer (M1) and four new chiral mesogenic monomers (M2～M5) containing menthyl groups were prepared. The chemical structures and purities of the target monomers were characterized with 1H NMR, FT-IR and elemental analysis, and specific optical rotations were evaluated with a polarimeter. Their structure-property relationships were discussed. The mesomorphic properties and phase behavior were investigated by differential scanning calorimetry and polarizing optical microscopy. The selective reflection wavelength of light was studied with UV/visible/NIR. The chiral monomers with more aryl segments showed lower specific optical rotation values. The monomers M2～M5 formed the mesophases when a flexible spacer was inserted between the rigid mesogenic core and the terminal menthyl groups by reducing the steric effect. M1 did not show any texture, and M2～M5 showed enantiotropic broken fan-shaped chiral smectic C (SC*) phase, and oily streak texture and focal conic texture of cholesteric phase. Moreover, M5 also exhibited platelet texture of a cubic blue phase on cooling cycles. With increasing temperature, the selective reflection of light shifted to the long wavelength region in the SC* phase range, and the short wavelength region in the cholesteric phase range, respectively. The melting and clearing temperatures increased, and the mesophase temperature range widened with increasing rigidity of the mesogenic core. Moreover, the ester linkage bond and aryl arrangement in the mesogenic core also affected the mesophase behavior.

Key words: menthyl group, liquid crystalline monomer, chiral smectic C phase, cholesteric phase, blue phase