Investigation of luminescent and liquid crystalline properties of the supramolecular hydrogen bonded complexes formed from non-mesogenic pyridine derivatives and lauric acid

Abstract

Hydrogen bonds are the best non-covalent interactions for building supramolecular structures. Nowadays, hydrogen bonded supramolecular liquid crystals are quickly evolving into a versatile, simple, and affordable method for new smart materials. Therefore, through intermolecular hydrogen bond interactions, a homologous series of supramolecular mesogenic systems are prepared in the present study. The non-mesogenic hydrogen bond acceptors i.e. 2-(4-alkoxyphenyl)-5-(pyridin-4-yl)-1,3,4-oxadiazoles (OXn) are synthesized, the structures are confirmed using various techniques (1H NMR, 13C NMR, ESI-MS, and elemental analysis) and their photophysical properties are studied in the solid state as well as in solution state. Moreover, the DFT study indicated the planar structure with greater intramolecular charge transfer between donors and acceptors. In addition, these molecules (OXn) are made to form a hydrogen bond with the non-mesogenic fatty acid i.e. Lauric acid (LA). The formation of the hydrogen bonds in the prepared supramolecular complex (OXn/LA) is confirmed by using the ATR-IR analysis. Further, red shifted solid state emission spectra are noted for the complexes (OXn/LA) compared to the parent molecules (OXn). The mesogenic properties of the prepared OXn/LA complexes are studied via differential scanning calorimetry, polarized optical microscopy, and X-ray diffractometry. It was found that the complexes OX-8/LA and OX-10/LA exhibit monotropic SmA mesophase, however, the remaining complexes are non-mesogenic in nature.