Preparation via a NHC Dimer 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(μ-OMe)­(η4-COD)]2 (1; COD = 1,5-cyclooctadiene) with 5-tert-butyl-1,3-bis­(3-isopropylimidazolium)­benzene diiodide ([iPrHImC6H3(5-tBu)­HImiPr]­[I]2), in the presence of KI, leads to [IrI­(μ-I)­{κ3-C,C,C-[iPrImC6H2(5-tBu)­ImiPr]}]2 (2). This complex reacts with 2-(1H-imidazol-2-yl)-6-phenylpyridine (HNImpyC6H5) and 2-(1H-benzimidazol-2-yl)-6-phenylpyridine
(HNBzimpyC6H5), in the presence of Na2CO3, to afford the bis­(tridentate) derivatives Ir­{κ3-C,C,C-[iPrImC6H2(5-tBu)­ImiPr]}­{κ3-N,N,C-[NImpyC6H4]} (4) and
Ir­{κ3-C,C,C-[iPrImC6H2(5-tBu)­ImiPr]}­{κ3-N,N,C-[NBzimpyC6H4]}
(5). Complexes 4 and 5 are
phosphorescent emitters (λem 482–590 nm),
which display observed lifetimes in the range 1.2–11.7 μs.
They show high quantum yields in both doped poly­(methyl methacrylate)
films and in 2-methyltetrahydrofuran at room temperature (ϕ
= 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 λmax of 552 nm and a maximum external quantum efficiency (EQE)
of 12%.