Hydrogen-bonded liquid crystal complexes: A comprehensive study of structure, behaviour and potential applications

Intermolecular hydrogen bond (HB) interaction becomes an intensively studied topic in supramolecular chemistry and soft matter science. Herein, a new series of hydrogen-bonded liquid crystals (HBLCs) composed of 3flurobenzoic acid derivatives (nOBAF) and 1,4-diazabicyclo [2.2.2] octane (DABCO) has been prepared and characterized by Fourier-transform infrared spectroscopy. The thermal behavior was determined by differential scanning calorimetry and observed by polarized optical microscopy. All complexes were found to exhibit smectic G (SmG) and smectic B (SmB) phases over a wide temperature range. Furthermore, it was found that the thermal stability of these mesophases increases with increasing the alkoxy chain length. The complex dielectric permittivity was reported as a function of frequency in the range 1 Hz-10 MHz. Lower frequency process attributed to the collective fluctuations of azimuthal angle and higher frequencies, associated to the soft mode were observed in SmB. In the SmG, additional to the soft mode (106 Hz) a higher frequency mode (105 Hz) was detected for the first time. The experimental results obtained for these complexes were correlated with density functional theory (DFT) calculations. Furthermore, these results suggest that nOBAF/DABCO has the potential to be switchable dielectric materials.