Phase polymorphism and thermal stability of new cholesterol thioesters derivatives

We report the fundamental properties of a series of new mesogens with cholesteric esters, cholesteryl 4-(4-alkoxybenzoylothio)benzoates C(n)H(2n+1)OC(6)H(4)COSC(6)H(4)COOch, where ch=cholesteryl, for n=7-10, nOSBch in short. They share a common feature, which is a high temperature cholesteric mesophase. In addition, the n=10 compound has a monotropic ferroelectric smectic C* phase. The chemical structure and purity of nOSBch were confirmed by standard methods: H-1 nuclear magnetic resonance (NMR), C-13 NMR, Fourier transform infrared spectroscopy and elemental analysis. Differential scanning calorimetry (DSC), polarising optical microscopy and transmitted light intensity were used to study the polymorphism of these mesogens. The substances were proved stable up to 240-270 degrees C (thermal stability deduced from DSC scans). The crystal structures were determined from X-ray diffraction data. Possible conformational disorder as well as nearest-neighbours intermolecular interactions were inferred from quantum chemical calculations.