Deuterated lactic acid derivative revealing re-entrant smectic A phase studied by 2NMR and dielectric spectroscopy

Liquid crystals as self-assembling systems may exhibit the re-entrancy phenomena occurring due to different competing interactions. Formerly, a homologue of lactic acid derivatives nZBL was described to exhibit a re-entrant smectic A phase (SmARE) below the ferroelectric smectic C* phase. Herein, we synthesised and studied a selectively deuterated compound, 9ZBL-D2, analogous to the previously studied homologue showing the re-entrance phenomenon. We confirmed that the deuterated compound 9ZBL-D2 exhibits analogous mesomorphic properties including the re-entrant SmARE phase. We concentrated on re-entrance phenomenon as the enantiotropic character of the SmARE phase enabled us to elucidate the orientational order and molecular dynamics in detail. We applied dielectric measurements and deuterium NMR (2H NMR) spectroscopy, and DSC and x-ray measurements to describe the mesomorphic properties of 9ZBL-D2. The analysis of 2H NMR spectra coupled with the study of the trend of spin-lattice relaxation times was performed to investigate the phase transitions of 9ZBL-D2 sample. The experimental data have been analysed and discussed.