Preparation via a NHC Dinner Complex, Photophysical Properties, and Device Performance of Heteroleptic Bis(tridentate) Iridium(III) Emitters

The preparation, photophysical properties, and applicability to the fabrication of organic light-emitting diodes (OLEDs) of new phosphorescent bis(tridentate) [5t + 4t'] iridium(III) molecules are described. Treatment of [Ir(mu-OMe)(eta(4)-COD)]2 (1; COD = 1,5-cyclooctadiene) with 5-tert-butyl-1,3-bis(3-isopropylimidazolium)benzene diiodide ([(i)PrHImC(6)H(3)(5-Bu-t)HIm(i)Pr][I](2)), in the presence of KI, leads to [IrI(mu-I){kappa(3)-C,C,C-[(i)PrImC(6)H(2)(5-Bu-t)Im(i)Pr]}](2) (2). This complex reacts with 2-(1H-imidazol-2-yl)-6-phenylpyridine (HNImpyC(6)H(5)) and 2-(1H-benzimidazol-2-yl)-6-phenylpyridine (HNBzimpyC(6)H(5)), in the presence of Na2CO3, to afford the bis(tridentate) derivatives Ir{kappa(3)-C,C,C-[(i)PrImC(6)H(2)(5-Bu-t)Im(i)Pr]}{kappa(3)-N,N,C-[NImpyC(6)H(4)]} (4) and Ir{kappa(3)-C,C,C-[(i)PrImC(6)H(2)(5-Bu-t)Im(i)Pr]}{kappa(3)-N,N,C-[NBzimpyC(6)H(4)]} (5). Complexes 4 and 5 are phosphorescent emitters (lambda(em) 482-590 nm), which display observed lifetimes in the range 1.2-11.7 mu s. They show high quantum yields in both doped poly(methyl methacrylate) films and in 2-methyltetrahydrofuran at room temperature (phi = 0.73-0.49). Complex 5 has been demonstrated to be suitable for use as a reasonably efficient phosphorescent greenish yellow emitter for OLED devices with an electroluminescence lambda(max) of 552 nm and a maximum external quantum efficiency (EQE) of 12%.