It is well established that phosphorescence in aromatic carbonyls occurs within about 1 ms when T1 has 3 n* character, but it takes longer than 100 ms when this state is a 3 *. We concluded that the main reason for this difference is that a direct SOC mechanism modulated by permanent dipoles couples T1 and S0 when the triplet minimum is 3 n*. However, the coupling mechanism in 3 * systems is indirect, involving weak transition dipole moments to highly excited states. The selection rules leading to this explanation are strictly valid for specific point groups and require that the 3 * state is totally symmetric. The reason for the difference in the phosphorescence lifetimes is not explained by the El-Sayed rule, as sometimes stated, but it is connected to it.