Hierarchical chirality transfer and thermally induced supramolecular chirality inversion in cholesteryl schiff-base liquid crystal dimers

A new series of nonsymmetric cholesterol-based Schiff-base liquid crystal dimers has been designed by linking a cholesteryl unit to a two-ring Schiff-base mesogenic core through flexible alkylene spacers to investigate the combined influence of spacer architecture and terminal chirality on mesophase evolution and supramolecular organisation. Sixteen dimers were synthesised across two chiral-tail series, namely, citronellyloxy (CSBC) and octan-2-yloxy (CSBO), each comprising corresponding R- and S-enantiomeric pairs with systematically varied spacer lengths. The compounds were fully characterised by spectroscopic and microanalytical techniques, while their mesomorphic behaviour was investigated using polarised optical microscopy (POM), differential scanning calorimetry (DSC), variable-temperature X-ray diffraction (XRD), and circular dichroism (CD) spectroscopy. All sixteen dimers exhibited enantiotropic liquid crystallinity with phase sequences comprising chiral nematic (N*), smectic A (SmA), chiral smectic C (SmC*) and twist grain boundary (TGB) phases, depending on spacer length and terminal chiral substituent. XRD studies confirmed monolayer SmA organisation together with tilted SmC* structures, establishing clear correlations between spacer architecture and molecular packing. Temperature-dependent CD investigations revealed mirror-image spectra for the corresponding R- and S-enantiomeric pairs and, most significantly, uncovered a thermally induced supramolecular chirality inversion (TISCI) during the N→SmC ** phase transition. The simultaneous reversal of both the selective reflection and chromophore absorption CD bands demonstrates that molecular stereochemistry remains unchanged while the supramolecular helix reverses its handedness through thermally driven molecular reorganisation. This hierarchical chirality switching establishes TISCI as a direct manifestation of chirality transfer across multiple structural length scales and provides new molecular design principles linking spacer architecture, terminal chirality and supramolecular organisation for the development of responsive chiroptical soft materials, photonic systems and advanced electro-optical liquid crystals.