Series of elongated azo esters containing three rings with methyl moiety as one of the terminal carbon chain and various substituents R(R=H,CH3,OCH3,NO2,Cl) at the other end of the molecule have been isolated , and their structure were were characterized by 1H-NMR and IR as well as elemental analysis . The mesomorphic properties of these compounds were investigated via differential scanning calometry and polarizing microscopy . . The thermal data indicate that all of these compounds exhibit mesomorphic properties (Nematic phase).The group efficiency order for the Nematic phase thermal stability can be derived for the compounds as : NO2>OCH3>CH3>Cl, With Density Functional Theory (DFT), we have calculated the electronic the electronic structures for azo compounds and the effects of the terminal groups in the azo liquid crystallaine compounds on the electronic structure have been discussed .Our results indicate that the energy differences between the lowest unocupied molecular orbit and the highest occupied molecular orbit are predominantly affected by the terminal groups of the azo liquid crystalline compounds.