The homologous series of 4-cyano-4′-phenyl-phenol-alkanoates (nCOOCB) was studied under the influence of terahertz (THz) frequency range. The nCOOCB series has a re-entrant nematic phase, which is suitable for electro-optical properties under the THz frequency. The birefringence and order parameter expresses the twisting of the nematic phase at the higher frequency range. The director angle has fluctuated at a higher frequency range. The refractive index has remained constant at a higher frequency. The ionisation potential, electron affinity and Homo-Lumo energy gap continuously decrease with an extension of alkyl chain length; however, the dipole moment increases. The Homo-Lumo energy bandgap is reciprocal to the dipole moment.