To explore the distribution patterns of molecular orbitals of HOMO and LUMO, we examined the FMO of the PPAB molecules in Acetonitrile solvent using the polarizable continuum model, as illustrated in Figure . It is clear based on the FMO analysis that the HOMO densities of all PPAB molecules exhibit similarity as they are distributed over the donor moiety, indicating a π-bonding nature and the LUMO densities are dependent upon the electron-withdrawing moieties, exhibiting a π-antibonding nature. The chemical stability, electrical, and optical characteristics of molecules are also reportedly correlated well using FMO analysis. Compounds with a lower HOMO-LUMO energy gap have higher chemical reactivity, and these compounds are highly polarizable, showing excellent NLO properties because of higher possibility of ICT. The FMO analysis is done in three solvents with different polarity as well to study the effect of polar solvent on the HOMO-LUMO energy gap. Furthermore, energy gaps (ΔEHL) of the HOMO to the LUMO are shown in Table .