Mechanism Studies on the Chemical Stability of FIrpic, a Typical Blue Phosphorescent Emitter for Electroluminescence, in the Redox States

Iridium(III)bis[2-(4,6-difluorophenyl)pyridyl-N,C^2′]picolinate (FIrpic) is a widely used light-blue phosphorescent material known for its favorable redox activity. However, the operational lifetime of FIrpic-based phosphorescent organic light-emitting diodes (PhOLEDs) remains unsatisfactory. To gain a deeper understanding of the chemical stability of FIrpic in various redox states, we explored its degradation mechanisms in the ground (S₀), one-electron oxidized (Ox.), and one-electron reduced (Re.) states using theoretical methods. Density functional theory (DFT) static calculations, combined with atomic center density matrix propagation (ADMP) simulations at temperatures of 500, 600, and 700 K, revealed that the cleavage of the Ir–N₁ bond is a crucial step in the chemical degradation process of FIrpic in both the ground and redox states. This bond breakage leads to a nonemissive five-coordinated trigonal bipyramidal intermediate. The degradation process is notably more facile in the redox states, particularly in the Re. Charge analysis indicates a decreasing trend in electronic delocalization between the LP_N electron donor natural bond orbital (NBO) and the d*_N–Ir(pic.) electron acceptor NBO, with the order S₀ > Ox. > Re. Our findings provide a deeper insight into the degradation mechanisms of FIrpic under different redox conditions. This understanding is crucial for the design of more stable materials in FIrpic-based PhOLEDs.