Evolution of Anisotropy, First Order Hyperpolarizability and Electronic Parameters in p-Alkyl-p'-Cynobiphenyl Series of Liquid Crystals: Odd-Even Effect Revisited

The homologues of p-alkyl-p'-cynobiphenyl (nCB) liquid crystal series are widely known for their diverse applications in display device industries, due to the low transition temperature. The transition temperature dependence on the number of carbon atoms in the alkyl chain, associated at one end of nCB series is commonly referred to as 'the odd-even effect', which is widely reported for the nematic zone (n <= 8). Herein, we perform a theoretical study on the odd-even effect in the homologues of nCB series for n = 1-12 using density functional based calculations at B3LYP/6-311++G(d,p) level. We have calculated electro-optical parameters such as the dipole moment, polarizability, anisotropy and hyperpolarizability along with some electronic parameters such as ionization potential, electron affinity, chemical hardness and absolute electronegativity of nCB mesogenic series. The variation of these parameters suggests that the odd-effect in nCB homologues is not only confined to nematic zone but also extended to smectic zone (n > 8) at the molecular level, except the variation of electron affinity which indeed suggests that the odd-even effect is limited to nematic zone. This study may offer better insights into properties of homologues of nCB and similar compounds at the molecular level.