Homoleptic Iridium(III) Compounds Bearing Bulky Bipyridine Ligand for Potential Application to Organic Light-emitting Diodes

摘要

Two sky-blue phosphorescent iridium compounds, fac-tris(2',6'-diisopropoxy-2,3'-bipyridinato)-N,C~4')Ir (III) (1) and fac-tris(2',6'-diisopropoxy-4-tert-butyl-2,3'-bipyridinato)-N,C~4)Ir(III) (2), were synthesized by a one-pot reaction of a reactive Ir(I) compound with a corresponding bipyridine ligand, to investigate their photophysical and electrochemical properties for potential application to white organic light-emitting diodes (WOLEDs). Their structures were confirmed by varied spectroscopic methods. Results indicated that both compounds possess facial geometry. The absorption, emission, thermal stability, and electrochemical properties were also investigated systematically. The two compounds showed sky-blue emission with λ_(max) = 462-463 nm; their photoluminescence quantum efficiencies relative to that of FIrpic were ～0.3-0.4. Compound 2 with a bulky substituent displayed the suppression of concentration quenching at high concentration, and its emission was less shifted to longer wavelengths compared to compound 1. Owing to the bulky substituent, the quantum efficiency of 2 is higher than that of its nonsubstituted counterpart. Therefore, the introduction of the bulky substituent in the ligand framework is an important strategy for developing high-efficiency blue phosphorescent materials. The two compounds developed in this study show high thermal and electrochemical stability, making them suitable candidates for OLED applications.