Optical and thermal properties of cholesteric solid from dicholesteryl esters of diacetylenedicarboxylic acid

Abstract

Dicholesteryl esters of diacetylenedicarboxylic acid with different lengths of methylene linkages were synthesised. Compounds with (CH ₂ ) _n (n = 2, 4, 5, 6, 7, 8, 10) showed a cholesteric phase. Phase transition temperatures from the isotropic phase to the anisotropic phase showed an odd–even effect of the number of (CH ₂ ) units. By rapid cooling from the cholesteric phase to 0 °C, the compounds were solidified retaining the cholesteric colours (cholesteric solid), some of which were stable at room temperature. Changing the temperature at which rapid cooling started changed the colours of the cholesteric solid. The thermal stability of the cholesteric solid also showed an odd–even effect of the number of (CH ₂ ) units. The effect can be explained by the difference in the stable structures of the molecules and the strength of the weak intermolecular interactions via carbonyl groups between the compounds with odd and even (CH ₂ ), which was observed in the FT-IR spectra.