2PA is a third-order nonlinear process, the simultaneous absorption of two photons of similar energy is called as two photon absorption. The increase in the percentage of the CT nature in a molecule has also reported to increase the 2PA cross-section. The 2PA cross-section is typically determined using the Goppert Mayer (GM) unit. The relationship between the GM and atomic unit is determined by the following equation 13. 𝛿 = δ