Optical and liquid crystalline properties of dicholesteryl derivatives having different configurations of the hydrocarbon linkages

The liquid crystalline and optical properties of four dicholesteryl derivat ives having various linkage configurations, but with the same number of con necting carbons (18), have been investigated, using differential scanning c alorimetry, polarizing optical microscopy, Fourier transform infrared (FTIR ) spectroscopy and UV-Vis spectroscopy. Quite different phase behaviours an d optical properties have been found for these compounds, while all of them exhibited the behaviour specific for a cholesteric phase. By rapid cooling from the cholesteric phase to 0 degrees C, the iridescent colours of some of the dicholesteryl esters were fixed in the cholesteric glassy state. It was difficult but possible to fix various stable colours in the cholesteric glassy state of one compound with a polymethylene (CH2)(18) linking chain. It was much easier to fix less stable colours for samples with the linking groups (CH2)(6) and C=C double bonds between them. Very unstable colours c ould also be fixed for the compound with the (CH2)(7) chains and a diyne gr oup. The fourth compound with a branched linking chain gave a cholesteric p hase which showed colours at room temperature. FTIR spectroscopy measuremen ts provided interesting results concerning the average change in molecular configuration between the blue cholesteric glass and the crystal for the co mpound with the (CH2)(7) polymethylene chains which crystallized within a f ew hours; also frequency changes associated with some bands were found and reported.