Unravelling the Mechanism of Excited-State Interligand Energy Transfer and the Engineering of Dual Emission in [Ir(CN)(NN)] Complexes.

Fundamental insights into the mechanism of triplet-excited-state interligand energy transfer dynamics and the origin of dual emission for phosphorescent iridium(III) complexes are presented. The complexes [Ir(CN)(NN)] (HCN = 2-phenylpyridine (-), 2-(2,4-difluorophenyl)pyridine (-), 1-benzyl-4-phenyl-1,2,3-triazole (-); NN = 1-benzyl-4-(pyrid-2-yl)-1,2,3-triazole (pytz, ), 1-benzyl-4-(pyrimidin-2-yl)-1,2,3-triazole (pymtz, ), 1-benzyl-4-(pyrazin-2-yl)-1,2,3-triazole (pyztz, )) are phosphorescent in room-temperature fluid solutions from triplet metal-to-ligand charge transfer (MLCT) states admixed with either ligand-centered (LC) (, , and ) or ligand-to-ligand charge transfer (LL'CT) character (, , and -). Particularly striking is the observation that pyrimidine-based complex exhibits dual emission from both MLCT/LC and MLCT/LL'CT states.