Phosphorescent Complexes

If you are into phosphorescent transition metal complexes here is a paper for you: The triplet state of organo-transition metal compounds. Triplet harvesting and singlet harvesting for efficient OLEDs by Yersin et al. It was very interesting to read this. They just give a relly nice picture of spin-orbit coupling effects and how they are affected by the ligand field. As a major effect: if the ligand field allows for quasi-degenerate states (e.g. octahedral complexes), then the zero-field splitting will be much stronger than in other cases (e.g square planar). And later on they show that the zero-field splitting shows a strong inverse correlation with the phosphoresence lifetime. But on the other hand, if the zero field splitting is too strong, then the highest triplet substate will no longer be efficiently thermally populated, which is a problem since this is usually the state with the strongest emission strength. For this reason there is as of yet no triplet harvesting complex with a phosphorescent lifetime below 1 μs.

Of course, I do not know if it is all correct. But it is nice to see that people are actually taking their time to produce realistic models to explain their results.