Funct. Mater. 2025; 32 (4): 553-561.
Optical band gap as a physico-chemical characteristic of liquid crystal mixtures with specific interaction of component molecules
1Institute for Scintillation Materials, National Academy of Science of Ukraine, 60 Nauky Ave, 61072 Kharkiv
2Institute for Single Crystals, National Academy of Science of Ukraine, 60 Nauky Ave, 61072 Kharkiv, Ukraine
Liquid crystal (LC) systems based on 4-n-pentyl-4′-cyanobiphenyl (5CB) doped with non-mesogenic salicylaldoxime (SA) and resorcinol (RES), where one could expect non-trivial behavior due to specific intermolecular interactions, were studied using differential scanning calorimetry (DSC), UV-Vis and FTIR spectroscopy. It was shown that eventual formation of supramolecular complexes led to additional temperature stabilization of the nematic phase. This effect, which we noted earlier for SA, is much more pronounced for RES. In the latter case, an increase in the nematic-to-isotropic phase transition temperature by ~15 °С was observed at RES concentration of 12 % w/w (3 : 1 molar ratio). Basing on the UV absorption data in LC state and dilute solutions, the values of optical band gap (Eg) were determined for 5CB+SA and 5CB+RES as functions of temperature and the dopant content. The concentration dependence of Eg for the 5СВ+RES system shows an extremum at 3 : 1 molar ratio, which is consistent with DSC data. Possible structures of supramolecular aggregates were proposed, taking into account dipole-dipole interactions, hydrogen bonding between cyano- and OH-groups of the component molecules as well as steric factors facilitating their tightest packing.
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