Several new cholesterol derivatives, cholesteryl 2-cyanoethyl ether, cholesteryl 4-cyanobenzoyl carbonate and cholesteryl cyanoacetate were prepared and their liquid crystal properties were studied by means of polarizing optical microscopy and thermal analysis.
Among those derivatives, only cholesteryl cyanoethyl ether and cholesteryl 4-cyanobenzoyl carbonate were found to exhibit cholesteric liquid crystal characteristics. In order to observe their liquid crystal behaviors in applied electric field, those materials were blended with mixtures of cholesteryl chloride, cholesteryl nonanoate and cholesteryl oleyl carbonate in several different weight ratios and were placed between, in contact with, I.T.O-coated glass plates separated by 16 $\mu$ and then electric potential was applied. It was observed that liquid crystal mixtures including new cholesteric liquid crystals changed color from red to green by Bragg-like reflection in the lower electric potential range compared with well investigated cholesteryl chloride-based systems (for an instance, cholesteryl chloride: cholesteryl nonanoate: cholesteryl oleyl carbonate=30:30:40). It was particulary notable that green color phase which was not observed with the previously reported cholesteryl chloride-based systems was observed with the presently investigated systems was observed with the presently investigated systems. In general, the presently studied liquid crystal systems exhibited slow responding characteristic toward the change in electrical potential probably due to high viscosity.
