Although the electronic transition of the crucial excited state associated with the maximum absorption originates mainly from frontier molecular orbitals (FMOs), they do not contribute entirely, so it is incomplete to examine transition only by HOMO and LUMO. In this case, performing hole-electron analysis is very practical for exploring the electronic excitation characteristics . The isosurfaces and hot maps of The first hyperpolarizability of molecules reflects the nonlinear relationship between molecular polarization and field intensity when subjected to an electric field, and is a critical parameter for describing the NLO response of molecules. The total amounts of the first hyperpolarizability (β0(-2ω;ω,ω)), the projection of the first hyperpolarizability and, respectively. The β0(-2ω;ω,ω) of the C18 derivatives are graphically shown in Figure . The β0(-2ω;ω,ω) of the H-C18-NO2 in zero-frequency limit (λ = ∞ nm), i.e., β0(-0;0,0), is calculated to be 570 a.u., which is very close to the value of the H-C18-H (518 a.u.), indicating that the effect of introducing -NO2 group alone to the first hyperpolarizability is almost negligible. In contrast, the introduction of -NH2 can significantly increase the β0(-0;0,0) of the molecule, with a value of 2770 a.u. NH2-C18-NO2 exhibits excellent β0(-0;0,0) of up to 4462 a.u., which is significantly higher than that of the other three derivatives and almost 8.6 times the corresponding value of H-C18-H. This is clearly due to the synergistic effect of electron donor and electron acceptor on the intramolecular charge transfer in the system. It is worth mentioning that the static β0(-2ω;ω,ω) of p-nitroaniline (pNA, NH2-C6H4-NO2), a typical D-π-A molecule, measured by gas-phase experiment is 1400 a.u., which is much smaller than the calculated values of NH2-C18-H and NH2-C18-NO2. This demonstrates the excellent optical nonlinearity of the C18 derivatives designed in this work, especially NH2-C18-NO2.