Effect of Length of Alkyl Group on Thermal-Liquid Crystalline Properties of Cholesteryl 4-n-Alkoxybenzoate

In this study, cholesteryl 4-n-alkoxybenzoates (Chol-n), with alkyl groups used for controlling the temperature of transition to the liquid crystal phase, were synthesized, and the effects of the length of the alkyl groups on the physical properties of the liquid crystal compounds were investigated. The chemical structures and thermal and liquid crystalline properties of the synthesized compounds were investigated by Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance spectroscopy (H-NMR), differential scanning calorimetry (DSC), and polarizing optical microscopy (POM). The synthesized compounds showed melting transition temperatures (Tm) in the range of 103 °C to 143 °C and all of the compounds except Chol-6 exhibited a wide liquid crystal phase temperature range of about 60 °C to 100 °C. No correlation between the number of carbon atoms in the molecule and the thermal properties of the compounds was found. All of the synthesized compounds showed an enantiotropic cholesteric phase, which was accompanied by a chiral smectic phase in the compounds Chol-6, Chol-8, Chol-9, and Chol-10. All of the compounds exhibited thermochromism in the liquid crystal state, and their color changed from red to blue as the temperature was increased.