A multifunctional iridium-carbazolyl orange phosphor for high-performance two-element WOLED exploiting exciton-managed fluorescence/phosphorescence

By attaching a bulky, inductively electron-withdrawing trifluoromethyl (CF₃) group on the pyridyl ring of the rigid 2-[3-(N- phenylcarbazolyl)]pyridine cyclometalated ligand, we successfully synthesized a new heteroleptic orange-emitting phosphorescent iridium(III) complex [Ir(L ₁)₂(acac)] 1 (HL₁ = 5-trifluoromethyl-2-[3-(N- phenylcarbazolyl)]pyridine, Hacac = acetylacetone) in good yield. The structural and electronic properties of 1 were examined by X-ray crystallography and time-dependent DFT calculations. The influence of CF₃ substituents on the optical, electrochemical and electroluminescence (EL) properties of 1 were studied. We note that incorporation of the carbazolyl unit facilitates the hole-transporting ability of the complex, and more importantly, attachment of CF₃ group provides an access to a highly efficient electrophosphor for the fabrication of orange phosphorescent organic light-emitting diodes (OLEDs) with outstanding device performance. These orange OLEDs can produce a maximum current efficiency of ∼40 cd A^-1, corresponding to an external quantum efficiency of ∼12% ph/el (photons per electron) and a power efficiency of ∼24 lm W^-1. Remarkably, high-performance simple two-element white OLEDs (WOLEDs) with excellent color stability can be fabricated using an orange triplet-harvesting emitter 1 in conjunction with a blue singlet-harvesting emitter. By using such a new system where the host singlet is resonant with the blue fluorophore singlet state and the host triplet is resonant with the orange phosphor triplet level, this white light-emitting structure can achieve peak EL efficiencies of 26.6 cd A^-1 and 13.5 lm W^-1 that are generally superior to other two-element all-fluorophore or all-phosphor OLED counterparts in terms of both color stability and emission efficiency.