This work analyzed the phosphorescence lifetime of aromatic carbonyl compounds. We aimed to explain the difference between 3 n* and 3 * emissions and estimate the importance of vibronic contributions. We addressed these questions by combining formal analysis of the selection rules controlling the singlet-triplet transition dipole moments and simulating vertical and vibronicallycorrected phosphorescence lifetimes for benzaldehyde and three derivatives. These systems range from 3 n* to 3 * T1 minimum, enabling a quantitative assessment of the different coupling mechanisms contributing to light emission.