A structural transformation of calamitic to discotic in cyanobenzene-cholesterol based trimers

We report the synthesis and investigations of new series of cholesterol-based liquid crystalline trimers. The materials consist of 2,3,4-trihydroxy benzonitrile core connected to three arms of cholesterol-based moiety with aliphatic spacers having different number of carbon atoms (<i>n</i>). The molecular structures were confirmed using different spectroscopic techniques. The molecular self-assembly of the trimers was investigated via differential scanning calorimetry (DSC), polarised optical microscopy (POM) and X-ray diffraction (XRD). The length of the spacer units significantly influences the observed liquid crystal (LC) phases. For homologues with spacer lengths <i>n</i> = 3 − 8, a chiral smectic phase (SmC*) was consistently observed. However, for the longest spacer (<i>n</i> = 9), a columnar LC phase emerged. This transition is attributed to the self-assembly of the half-discoid molecules into columnar mesophases, likely driven by strong polar interactions and pronounced dipole moments, which promote alignment and organisation into a more ordered, columnar structure. UV-Visible aggregational analysis reveals the presence of strong <i>H</i>-aggregates. The reported polar-interacting discotic structure could be of interest in optoelectronic and sensing technologies.