Insight into the Phosphorescent Process of Cyclometalated Ir(III) Complexes: Combination of the Substituents on Primary and Ancillary Ligands Controls the Emission Rule and Quantum Yield

Rare high-efficiency deep blue organometallic phosphors are one of the major roadblocks to develop the white organic light-emitting diodes (OLEDs). In this article, the phosphorescent properties of four potential blue emitting cyclometalated (C boolean AND N) Ir(III) complexes (two experimental reported and two theoretical novel designed) are investigated by the density functional theory/time-dependent density functional theory (DFT/TDDFT) method to explore the cooperative effect of the electron-withdrawing substituent on the primary ligand associated with different ancillary ligands. The origins of emission are identified by means of DFT and TDDFT calculations including spin orbit coupling (SOC). The theoretical results indicate that emissions from the higher lying triplet state also have a contribution. The radiative rate constant (k(r)) is quantitatively determined. To further elucidate the phosphorescent decay process, the SOC matrix elements, singlet triplet splitting energies, and transition dipole moments are calculated to evaluate the radiative process. Both the temperature-independent and temperature-dependent nonradiative decay processes are considered. The calculated results testify that the incorporation of the electron-withdrawing group heptafluoropropyl (HFP) is not insurance to improve the quantum yield. The substituents on the primary ligand should be combined with the suitable ancillary ligand to enhance the quantum yield.