Intertwined spontaneous helix formation in achiral bent-core liquid crystals

Inspired by several reports of spontaneous helix formation in bent-core smectics, we have investigated the smectic phases of a series of bent-core mesogens with 4-cyanoresorcinol bisbenzoate cores. In PAL30, the homolog with n=14 alkyl tails, we observed an incommensurate, bent-core phase with a single helix incommensurate with the smectic layering [1], a structure broadly analogous to the phase of rod-shaped molecules. In the PAL29, the n=16 homolog, we have confirmed, using both resonant and non-resonant x-ray diffraction, as well as electro-optical methods, the existence of a phase with intertwined helices, similar to the structure recently reported by Salamonczyk and co-workers [2]. Establishing the existence of the intertwined double-helical phase and the single-helical phase in such closely related homologs is an important step in understanding the competing interactions that lead to such exotic phase structures.
[1] A. Green et al., PRL 122, 107801 (2019).
[2] M. Salamonczyk et al., Nature Communications 10, 1922 (2019).