Induced Smectic-A phase at low temperatures through self-assembly

Self-assembled Smectic-A liquid crystals (LCs) are synthesized with low molar mass non-mesogenic moieties through intermolecular Hydrogen Bonding (HB) interactions. The HB complexes viz., PyBnA:xClBA (where n = 10, 14 and 16; x = 2, 3 and 4) are exhibiting an orthogonal Smectic-A (SmA) mesophase over a wide range of temperatures and towards ambient temperatures. The proton donors in these complexes, chloro substituted benzoic acids viz., 2-chloro, 3-chloro and 4-chloro benzoic acids (xClBA, x is the position of chlorine on the benzoic acid) are non-mesogenic. The proton acceptors, (4-pyridyl)-benzylidene-4′-n-alkyl anilines (decyl, tetradecyl and hexadecyl) (PyBnA, n is no. of carbons in alkyl chain) are also non-mesogenic. The presence of HB between the proton donor and acceptor is confirmed by Fourier Transform Infrared spectroscopy. The characteristic textures of SmA in all the complexes are observed through Polarizing Optical Microscope (POM) in conjunction with a hot stage. The enthalpy changes across the phase transitions (Isotropic – SmA; SmA – Cryst.) are determined by Differential Scanning Calorimeter (DSC). The influence of chain length of proton acceptor and the position of substituent on proton donor on the thermal stability of smectic mesomorphism are studied. The results are compared with reported linear and non-linear HBLC complexes.

► The HB complexes are mesogenic whereas the proton donor and acceptor are non-mesogenic.
► All the complexes exhibit self-assembly behavior by forming the 1-D SmA mesophase.
► Mesomorphism at ambient temperatures with decreasing chain length of a proton acceptor.
► Room temperature SmA is realized in PyB10A:2ClBA complex.
► The substituent at para position of the proton donor is promoting the LC stability.