Figure shows the chemical structure of Ni(II) tetrakis(2,4,6-trimethylphenyl)porphyrin (NiTMP), where the methyl substituents are attached at the four meso position (S.I.1). Figure shows the geometric structure of the singlet ground state S 0 in toluene optimized with DFT (Neese2020,Neese2022) without symmetry constraint. The computational details are given in S.I.2. The complex is quasi-planar, with an average bond length NiN of 1.942 Å and an average out-of-plane (oop) ruffling dihedral angle CNNC of 29.84°. The electronic structure is characteristic of square planar Ni(II) complexes, with the central ion being in the (dπ) 6 (dz 2 ) 2 low spin (LS) configuration. Kohn-Sham orbitals are presented in S.I.2.