Anomalous Phosphorescence from an Organometallic White-Light Phosphor.

We report theoretical results on the possible violation of Kasha's rule in the phosphorescence process of (acetylacetonato)bis(1-methyl-2-phenylimidazole)iridium(III) and show that the anomalous emission from both the T1 and T2 states is key to its white-light phosphorescence. This analysis is supported by the calculated Boltzmann-averaged phosphorescence lifetime of 2.21 μs, estimated including both radiative and nonradiative processes and in excellent agreement with the experimentally reported value of 1.96 ± 0.1 μs. The T2 state is found to be of metal-to-ligand charge-transfer character (dπ → nπ), and the d orbital contribution comes from 5dz2 and 5dx2-y2, whereas the S1 and T1 states both have dπ-pπ character with significant 5dxz orbital contribution, allowing for efficient intersystem crossing from the S1 to the T2 state and, in turn, phosphorescence from the T2 state. Our results open new opportunities for tailoring the phosphorescence wavelength and thus the design of molecules with improved photovoltaic properties.