and BH&HLYP agree within ∼ 0.03 Å with each other, the bond lengths of the M06-2X-optimized structure are generally longer by ∼ 0.1 Å. Using these, the vertical excitation energies (VEEs) of both non-SOC and SOC (italic) states as calculated by various theories and the results are presented in Table . The GMC-QDPT2 results indicate that regardless of reference geometry, the relative state order is 3 nπ * < 3 ππ * < 1 nπ * . Except for M06-2X, the 3 nπ * by MRSF is slightly lower than 3 ππ * . However, unlike GMC-QDPT2, the relative state order of 1 nπ * is in between the two triplet states according to B3LYP, BH&HLYP and PBE0. In general, as seen in previous studies, the three states are nearly degenerate with each other and their relative orders are sensitive to the choice of theories.