Electronic structure and vibrational spectra of 1OCB liquid crystal: a DFT study

The molecular and thermodynamical properties of 4-n-methoxy-4′-cyanobiphenyl (1OCB), which is the first homologue of the 4-n-alkoxy-4′-cyanobiphenyl liquid crystal series, have been investigated. 4-n-methoxy-4′-cyanobiphenyl is a nematic liquid crystal which transforms from crystal to isotropic phase at 104°C and from isotropic to nematic phase at 85·5°C.The molecular geometry has been optimized by first-principles Hartree–Fock (HF)/6-31G(d,p) and density functional theory (DFT) Becke, three-parameter, Lee–Yang–Parr (B3LYP)/6-31G(d,p) methods using the General Atomic and Molecular Electronic Structure System program. The molecular electrostatic potential surface has been scanned with a 0·001 electrons/b³ isodensity surface. The highest occupied molecular orbital and lowest unoccupied molecular orbital energies and thermodynamic properties of the molecule such as internal energy, entropy, enthalpy and Gibbs free energy have been reported. Further, vibrational assignments of the molecule, carried out using first-principles HF/6-31G(d,p) as well as DFT B3LYP/6-31G(d,p) techniques, have been compared and discussed. Efforts have been made to understand the liquid crystalline behavior of the system.