All DFT optimizations were carried out using Turbomole program package V7.3. The electronic structure is further explored by performing single-point XMS-CASPT2 and state-specific (SS-)RASPT2 calculations for the two lowest singlet and triplet states with larger active spaces on the XMS-CASPT2, TPSSh-D3, and PBE0-D3 molecular geometries using the OpenMolcas program package. For the bare copper corrole, ANO-RCC basis sets were used with the following contractions: 7s6p5d3f 2g1h for copper, 4s3p2d1f for nitrogen, 4s3p1d for carbon, and 3s1p for hydrogen. Scalar relativistic effects were included through the second-order Douglas-Kroll-Hess (DKH2) Hamiltonian. For the triphenyl copper corrole, the same contractions were used for the copper, nitrogen, and carbon atoms within the corrole; however, smaller basis sets were used for the phenyl groups. Specifically, the basis set contractions for carbon and hydrogen atoms in the peripheral phenyl groups were 3s2p and 2s, respectively. An imaginary shift of 0.2 a.u. was used for the single-point XMS-CASPT2 and SS-RASPT2 calculations. Since the IPEA shift was not included in the geometry optimizations, it is also not included here to maintain a consistent choice in zeroth-order Hamiltonian. For those interested, selected results including the IPEA shift are included in (Table ). In addition to performing multireference calculations on the minimum energy structures, single-point calculations were performed along the PES generated by the linear interpolation internal coordinates (LIIC) between the S 0 and T 0 geometries for the XMS-CASPT2, TPSSh-D3, and PBE0-D3 geometries.