Theoretical study on the vibrationally resolved spectra and quantum yield of blue phosphorescent iridium(III) complexes with 2-(4-fluoro-3-(trifluoromethyl)-phenyl)pyridine as the cyclometalated ligand

In this paper, the phosphorescent properties of six Ir(III) complexes with 2-(4-fluoro-3-(trifluoromethyl)-phenyl) pyridine (4 F-3CF3ppyH) as the cyclometalated ligand (two experimentally reported and four novelly designed) are investigated by density functional theory (DFT) and quadratic response (QR) time-dependent density functional theory (TDDFT) including spin-orbit coupling (SOC). The vibrationally resolved phosphorescence spectra were calculated to elucidate the experimental spectra. The strongest emission peak is mainly contributed by 0-0 transition. The strong shoulder peak can be ascribed as benzene ring and pyridine ring skeleton fundamental vibration transitions coupled with C-H wagging vibration transitions. The wide and weak emission band arises from the combination frequency. It was found that all of the six compounds could emit blue phosphorescence. To obtain the quantum yields, the radiative rate constant is quantitatively determined, while the nonradiative decay rate is qualitatively evaluated both by temperature-independent and temperature-dependent nonradiative decay processes. It shows that the quantum yields of all the six compounds are very high, which are evaluated to exceed 0.85. As a result, all of them are expected to be potential blue-emitting Ir(III) complexes.