Direct spectroscopic observation of interligand energy transfer in cyclometalated heteroleptic iridium(III) complexes: A strategy for phosphorescence color tuning and white light generation

We have characterized a series of highly phosphorescent cyclometalated heteroleptic Ir(III) complexes containing emitting (chromophoric) ancillary ligands with appropriate triplet levels below that of the cyclometalating ligand. We directly observed relatively rapid (ca. 6-7 ns(-1)) exothermic interligand energy transfer (ILET) from the cyclometalating ligand to the emitting ancillary ligand by time-resolved spectroscopy, which afforded a novel strategy of emission color tuning. Characteristic ILET processes in the heteroleptic Ir(III) complexes were further elucidated by electrochemical measurements and the density functional theory calculations. Facile and efficient generation of white phosphorescence was demonstrated by exploring the ILET process in a mixture of heteroleptic Ir(III) complexes.