MOLECULAR ELECTRONIC STRUCTURE AND STRUCTURE–PROPERTY RELATIONSHIPS OF 5CB: A DISPERSION-CORRECTED DFT STUDY

Abstract

5CB (4-cyano-4′-pentylbiphenyl) is a thermotropic liquid-crystal molecule at the ωB97XD/6-311G(d,p) level whose elongated structure and terminal cyano group give the molecule marked geometric and electrostatic anisotropy. Its molecular and electronic properties were examined using DFT using the ωB97XD functional with the 6-311G(d,p) basis set. Frequency analysis of the optimized structure showed no imaginary frequencies. The HOMO was concentrated mainly on the biphenyl framework, while the LUMO extended further toward the cyano-substituted region. Their calculated energies were −8.34 and 1.64 eV, respectively, corresponding to a HOMO–LUMO separation of 9.98 eV. The 9.98 eV separation is interpreted here as a method-dependent frontier-orbital value rather than as an experimental optical band gap. The calculated dipole moment was 6.52 D, while the MEP surface showed the strongest electron-rich region around the cyano nitrogen. Together, molecular shape, aromatic electronic structure, and terminal polarity may influence intermolecular interactions and orientational organization. However, collective nematic behavior cannot be assessed directly from the isolated-molecule model.