Theoretical (DFT) and experimental studies on multiple hydrogen bonded liquid crystals comprising between aliphatic and aromatic acids.

Liquid crystalline complex has been designed from non-mesogenic citric acid (CA) and mesogenic 4-undecyloxybenzoic acid (11OBA) in different mole ratio by means of intermolecular hydrogen bond. Optimized geometry for CA + 11OBA (1:1) HBLC complex using density functional theory (DFT) at B3LYP level with 6-311G (d, p) basis set has been studied. Highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), hydrogen bond length/angle, electrostatic potential (ESP) and Mulliken charge distribution for the HBLC complexes are theoretically determined. Further atomic, molecular properties and charge transfer capability of present HBLC complex is evaluated from HOMO/LUMO energies. Theoretically calculated vibration frequencies of HBLC complex is validated through experimentally recorded Fourier transform infrared (FT-IR) spectrum. Characteristic features of various textures by polarizing optical microscopy (POM) and temperature dependent of various thermodynamic properties of CA + 11OBA complexes are carefully investigated. Enantiotropic nematogen and finger print smectic X textures along with their phase sequences are also analyzed. Structural and optical characteristics of present HBLC complexes are evinced by nuclear magnetic resonance ( 1 H NMR) and UV–Vis spectrophotometer (for band gap) techniques. The impact of mesogenic ratio (11OBA) on CA + 11OBA complex is also discussed. In this present work, a noteworthy observation of photocatalytic activity of CA + 11OBA HBLC complex is noticed. Also, textural changes with phase transition temperature, induced smectic phases, thermal range, enthalpy, and tilt angle are reported. Presence of H-bond in the HBLC complex and experimentally obtained results are compared with theoretical DFT studies. [ABSTRACT FROM AUTHOR]