The frontier molecular orbitals of TCP-BP-SFAC, 4CzTPNBu and DBP were optimized using the density functional theory (DFT) method with PBE0-D3 functional at the basis set level of 6-31G (d, p), and the natural transition orbitals of 4CzTPNBu were optimized using the time-dependent DFT method with PBE0-D3 functional at the basis set level of 6-31G (d, p). The above calculations were performed using Gaussian16 package. The MPI values, and natural transition orbital analysis were analyzed with Multiwfn.