Synthesis and mesomorphism of novel multi-arm liquid crystals with cholic acid as chiral centre linking Schiff base moieties as mesogens

A new series of multi-arm chiral liquid crystals (LCs) D1-D3 were synthesised and characterised. Cholic acid was used as the core and -[4-(p-alkoxybenzoloxy)phenoxycarbonyl]valeric acid (B1-B3) was used as the mesogenic arms, containing different terminal substituent X (B1: X= -OCH3, B2:X= -CH3, B3: X= -Cl). Their structures and mesomorphic properties were investigated by Fourier-transform infrared spectroscopy, nuclear magnetic resonance hydrogen spectrometer, differential scanning calorimetry, polarised optical microscopy and X-ray diffraction, respectively. The mesogenic B1-B3 displayed smectic B phase. The multi-arm LC D1 displayed cholesteric, while D2 and D3 exhibited nematic phase. The formation of cholesteric phase of D1 was affected by both the chiral core - the bulky cholic acid and the polarity of the terminal substituent of the mesogenic arm. That D1 displayed cholesteric phase but D2-D3 did not indicated that the stronger polarity of the terminal group OCH3 of D1 played an important part in stabilising the cholesteric phase. The multi-arm LCs D1-D3 all showed ultraviolet activity. The wavelength of maximum absorption of D1-D3 was affected by the terminal substituent of the mesogenic arm. [GRAPHICS] .