A first principles and mean field investigation of the conformational properties of 5CB

Although the minimum energy conformation of the mesogenic molecule 4-n-pentyl-4′-cyano-biphenyl (5CB) is known to have an inter-ring torsional angle of 37.0° and an alkyl tail which lies perpendicular to the adjoining phenyl ring, less is known about the conformational properties of the alkyl tail. This paper investigates these properties in both the gas and nematic phase by combining first principles density functional theory calculations with the surface tensor mean field model of Ferrarini et al. (Molec. Phys, 1992, 77, 1). By comparing gas and nematic phase conformer populations, it is found that the nematic mean field selectively favours and disfavours certain conformations of the tail. The conformer distribution is discussed with reference to the results of bulk simulation studies and to C—D bond order parameters measured by NMR experiments.