The PPAB core present in all three compounds (Figure ), and these molecules demonstrate a high level of resistance to degradation caused by light which is a phenomenon usually exhibited by inorganic framework containing NLO molecules. The π-conjugation bridge, which is in this case a thienyl or phenylene linker, promotes ICT. A π-conjugated linker is employed to establish a connection between both the electron-donating and electronwithdrawing groups in a molecule. This process leads to an improvement in the NLO properties of the molecules. Varying the nature of the donor groups and the π-conjugated bridge by means of chemical design is the most common strategy for tuning of the first hyperpolarizability (βtot). We also studied the second-order NLO properties of the PPAB molecules which form the basis for the designing of the NLO switching, among others.