Abstract
Summary Simply replacing pyridine in cyclometalating ligands in FIrpic with pyrimidine affords the complex MS 2 , which has a slight red-shifted emission but shorter excited-state lifetime and the capability to form a highly efficient blue phosphorescent organic light-emitting device (OLED) with long operation lifetime ( T 50 > 2,200 hr). Further replacement of the picolinate-based ancillary ligand of MS 2 with strong-field CF 3 -containing pyridine-azole ancillary ligands leads to bluer emitters ( MS 17 and MS 19 ) with nearly unitary photoluminescence quantum yield and preferential horizontal emitting dipole orientations (with horizontal dipole ratios of 75%–77%) beneficial for OLED optical out-coupling. OLEDs using MS 17 and MS 19 as emitters gave bluer emission and very high external quantum efficiency exceeding 31% yet with comparably short device lifetimes as FIrpic -based devices. Theoretical analysis indicates that the distinct stability of the MS 2 -based device might be attributed to its relatively large energy difference between 3 MC (metal center d-d transition) and 3 MLCT states.
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