New hydrogen-bonded liquid crystal supramolecular systems: role of (+ I)-alkoxy substituents in promoting molecular ordering

Abstract

AbstractNovel H-bonded liquid crystals (HBLCs) are synthesized and examined for their mesomorphic behavior. The HBLCs are prepared with Schiff base proton acceptors containing 8 and 18 carbons in the alkyl chain and the proton donor with 4-substituted benzoic acids. All the compounds exhibit smectic A mesophases, with one of the compounds exhibiting LC properties below 298 K. It is interesting to note that the ethoxy-substituted HBLCs exhibit a wide range of thermal stability. Density functional theory calculations revealed the formation of two hydrogen bonds between the substituted acids and the pyridine ring based on the orientation of the donor and the acceptor moieties. There are no significant changes observed in the hydrogen bond length with the increase in the chain length of the proton acceptor moiety, indicating the dilution of the cores by the longer alkyl chain lengths is compensated with the (+ I) effect of alkoxy substituents. Quantum chemical modeling studies on these molecules revealed the reduction in the HOMO–LUMO energy gap by approximately 0.3 eV for oxy-containing compounds, making them more chemically reactive by donating electrons (+ I) into the aromatic cores. These materials provide a significant breakthrough in designing innovative LC materials. This work is in support of the SDG-9 of the United Nations. Graphical abstract