We started this subsection by asking whether there was a connection between the El-Sayed rule and the phosphorescence lifetimes. The difference between phosphorescence lifetimes depends on a SOC selection rule that is slightly more general than the El-Sayed rule, as it does impose any restriction on the spatial configurations. Moreover, the phosphorescence lifetimes also depend on the singlet-triplet dipole moment difference. Therefore, it seems inadequate to attribute the phosphorescence lifetime difference to a consequence of the El-Sayed rule.