Luminescence of porphyrins and metalloporphyrins. Part 3.—Heavy-atom effects

The fluorescence quantum yields and lifetimes for a series of metal tetraphenylporphyrins were found to decrease with increasing spin–orbital coupling constant of the central metal ion. The triplet states gave similar effects at both 77 and 293 K, as shown by luminescence and flash photolysis studies. In particular, the triplet-state lifetimes decreased in the order Mg > Zn > Pd ≈ Cd > Hg and it was possible to relate the rate constants for non-radiative decay processes to the spin–orbital coupling constant of the metal ion although different metal ions interacted with the porphyrin π-system to a different extent.