Induced and enhanced mesomorphism through intermolecular hydrogen-bonding interactions: influence of rigid core and π–π interactions

A non-mesogenic proton acceptor, viz., (4-pyridyl)-benzylidene-4ʹ-n-heptyl aniline (PyB7A), is prepared and treated with non-mesogenic proton donors, viz., aliphatic and aromatic carboxylic acids, in a 1:1 molar ratio, and their mesomorphism is studied. The non-mesogenic aliphatic acids used are nonyl, undecyl, tridecyl, tetradecyl, hexadecyl and octadecanoic acids which are non-toxic, biodegradable and biocompatible; and the non-mesogenic aromatic carboxylic acids used are x-fluoro/x-chlorobenzoic acids (x is the position of the substituent, x = 2, 3 or 4). The proton donors and acceptors are non-mesogens and are involved in intermolecular hydrogen-bonding (HB) interactions, resulting a smectic mesomorphism. The HBs between the moieties were characterized by Fourier transform infrared (FTIR) spectroscopy. The mesomorphic thermal stabilities of the PyB7A:mA and PyB7A:x(F/Cl)BA HB complexes are discussed in comparison with the similar HB complexes viz., PyB14A:mA; PyB16A:x(F/Cl)BA; PyB16A:nOBA and nOBA dimers. The number of aromatic rings i.e., rigid cores and the π–π interactions in the HB complexes on the induced mesomorphism are discussed. This research supports sustainable production practices, advancing SDG 12.