is the energy of the T b state evaluated at the minimum of the S a state). The H ab couplings correspond to the SOCs computed as described above. For the energy difference between the states (∆E ab ) we used the difference between the energies of adiabatic states at the geometry at which the rates are computed (∆E ab = ∆E ad ab ). The estimation of (r)ISC rates is done based on the MS-6-CASPT2/CASSCF(14,11)/aug-cc-pVDZ energies and CASSCF(14,11)/aug-cc-pVDZ spin-orbit couplings.