Mesomorphic thermal stabilities in supramolecular liquid crystals: Influence of the size and position of a substituent

A new homologous series of supramolecular Hydrogen Bonded Liquid Crystalline (HBLC) materials are synthesized with two low molar mass non-mesogenic moieties. The non-mesogenic substituted benzoic acids viz., 2-fluorobenzoic acid (2FBA), 3-fluorobenzoic acid (3FBA) and 4-fluorobenzoic acids (4FBA) are used as the proton donors. Non-mesogenic proton acceptors, PyBnA viz., (4-pyridyl)-benzylidene-4′-n-alkyl anilines (decyl, tetradecyl and hexadecyl) are used for the formation of supramolecular structures with the above proton donors. The HB between the two moieties is confirmed by FTIR spectroscopy. All the complexes exhibiting the smectic mesomorphism are characterized by Polarizing Optical Microscope (POM) equipped with a hot stage. Differential Scanning Calorimeter (DSC) is used to determine the enthalpy change across the mesomorphic phase transitions. The effect of position of fluorine atom and the chain length of proton acceptor on the mesomorphic stability is studied. The mesomorphic thermal stabilities and their melting/clearing temperatures are discussed in the wake of the data available on other supramolecular HBLCs with and without electronegative substituents on the proton donor moieties.