Phosphorescent Properties of Heteroleptic Ir(III) Complexes: Uncovering Their Emissive Species

In this contribution, we assess thecomputational machinery tocalculate the phosphorescence properties of a large pool of heteroleptic[Ir(C<^>N)(2)(N<^>N)](+) complexes (where N<^>N is anancillary ligand and C<^>N is a cyclometalating ligand) including theirphosphorescent rates and their emission spectra. Efficient computationalprotocols are next proposed. Specifically, different flavors of DFTfunctionals were benchmarked against DLPNO-CCSD(T) for the phosphorescenceenergies. The transition density matrix and decomposition analysisof the emitting triplet excited state enable us to categorize thestudied complexes into different cases, from predominant triplet ligand-centered((LC)-L-3) character to predominant charge-transfer ((CT)-C-3) character, either of metal-to-ligand charge transfer ((MLCT)-M-3), ligand-to-ligand charge transfer ((LLCT)-L-3), or acombination of the two. We have also calculated the vibronically resolvedphosphorescent spectra and rates. Ir(III) complexes with predominant (CT)-C-3 character are characterized by less vibronically resolvedbands as compared to those with predominant (LC)-L-3 character.Furthermore, some of the complexes are characterized by close-lyingtriplet excited states so that the calculation of their phosphorescenceproperties poses additional challenges. In these scenarios, it isnecessary to perform geometry optimizations of higher-lying tripletexcited states (i.e., T-n). We demonstrate that in the latterscenarios all of the close-lying triplet species must be consideredto recover the shape of the experimental emission spectra. The globalanalysis of computed emission energies, shape of the computed emissionspectra, computed rates, etc. enable us to unambiguously pinpointfor the first time the triplet states involved in the emission processand to provide a general classification of Ir(III) complexes withregard to their phosphorescence properties.