The effect of dopant chirality on the properties of self-assembling materials with a ferroelectric order

Abstract

A series of achiral hockey stick-shaped molecules forming a tilted smectic I liquid crystal phase as well as one non-mesogenic chiral bistereogenic analogue were synthesized and characterized. Herein, we report an example of an achiral hockey stick-shaped compound exhibiting a smectic I phase with a direct transition to the isotropic phase for the first time. This occurrence was confirmed via polarized light microscopy, dielectric spectroscopy, and XRD studies. Homologues with an odd number of carbon atoms in the oligomethylene spacer chain exhibit a lower clearing point than members posessing an even number of carbon atoms in this chain; thus, a characteristic odd–even effect has been observed. The influence of the synthesized compounds with different degrees of chirality and similar chemical structures on the properties of the host compound with a chiral smectic C phase was investigated. A chiral compound forming a wide-temperature chiral smectic C phase without any additional mesophase and having a short helical pitch was selected as the host material for the creation of two bicomponent systems. The mesomorphism of each binary mixture was characterized using optical microscopy and differential scanning calorimetry. The helical pitch of every binary mixture, forming a chiral smectic C phase, was studied within its full phase temperature range. As expected, the chiral host compound in the smectic C* phase doped with the hockey stick-shaped mesogen exhibited a longer helical pitch and lower spontaneous polarization than the chiral host material. On the other hand, for the chiral host compound doped with a non-mesogenic analogue containing two chiral centres, the helical pitch was shorter, and the spontaneous polarization was higher. These results should be potentially applicable for the design of advanced functional multi-component mixtures useful for various applications. The mesogenic behaviour of one binary mixture, forming both the chiral smectic I and titled chiral smectic C phases, was deeply studied via X-ray diffraction and dielectric spectroscopy techniques.