To evaluate the PES between the two geometries, a scan of linearly interpolated internal coordinates (LIIC) between the S 0 and T 0 XMS-CASPT2 optimized geometries was performed for both complexes. At each set of coordinates, the energies of the S 0 , T 0 , S 1 , and T 1 states were computed using XMS-CASPT2(14e,15o) (Figure ). From the S 0 saddled structure, the two S 0 surfaces increase in energy as the geometry becomes less saddled until reaching the nearly planar T 0 structure. For both corroles, the S 0 state is multiconfigurational but the contributions of the configurations discussed earlier vary across the surface in which the multireference character decreases as the saddling angle decreases (Table -S13). On the other hand, the T 0 state remains single-reference throughout the LIIC surfaces. While very little differences is observed between the shapes of the ground state surfaces, the T 0 state lies closer in energy to the S 0 state for the unfunctionalized copper corrole than for the triphenyl copper corrole. As noted in the prior section, on the planar T 0 structure, the S 0 and T 0 states become degenerate in the unfunctionalized ligand but retain a small energy gap (2.2 kcal/mol) in the triphenyl-functionalized ligand that remains slightly saddled at the T 0 geometry (Table , S21). Some orbital mixing between the b 1 and d x 2 -y 2 orbitals remains in the S 0 state of the planar triphenyl copper corrole (Figure ). Moreover, the S 1 and T 1 states are lower in the unfunctionalized complex. Note that the active space used along the scan is larger than that used in the optimization. A similar picture emerges for the S 0 and T 0 states if the scan is repeated with the XMS-CASPT2(4e,5o) (Table and S17, Figure ). However, with the (4e,5o) space, the S 1 and T 1 surfaces are nearly degenerate in both complexes, although they are separated by the 1 to 2 kcal/mol in each geometry when the (14e,15o) active space is employed. Throughout the prior sections, the different nature of the S 0 state using XMS-CASPT2