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

Abstract

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)( 4 -COD)]2 (1; COD = 1,5cyclooctadiene) with 5-tert-butyl-1,3-bis(3-isopropylimidazolium)benzene diiodide ([ i PrHImC6H3(5-t Bu)HIm i Pr][I]2), in the presence of KI, leads to [IrI(μ-I){κ 3 -C,C,C-[ i PrImC6H2(5-t Bu)Im i Pr]}]2 (2). This complex reacts with 2-(1H-imidazol-2-yl)-6-phenylpyridine (HNIm-pyC6H5) and 2-(1H-benzimidazol-2-yl)-6-phenylpyridine (HNBzimpyC6H5), in the presence of Na2CO3, to afford the bis(tridentate) derivatives Ir{κ 3 -C,C,C-[ i PrImC6H2(5-t Bu)Im i Pr]}{κ 3 -N,N,C-[NImpyC6H4]} (4) and Ir{κ 3 -C,C,C-[ i PrImC6H2(5-t Bu)Im i Pr]}{κ 3 -N,N,C-[NBzimpyC6H4]} (5). Complexes 4 and 5 are phosphorescent emitters (em = 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 ( = 0.73−0.49). Complex 5 has demonstrated to be suitable to be used as a reasonably efficient phosphorescent greenish-yellow emitter for OLED devices with electroluminescence max of 552 nm and maximum external quantum efficiency (EQE) of 12%.

Preparation and Photophysical Properties of Bis(tridentate) Iridium(III) Emitters: Pincer Coordination of 2,6-Di(2-pyridyl)phenyl

“…The Ir-aryl5t and Ir-aryl4t' bond lengths of 1.933 6Å (Ir-C(32)) and 2.031(6) (Ir-C(1)) Å, respectively, compare well with those of 6 and 7. In the 13 C{ 1 H} NMR spectrum, the resonances corresponding to the metalated carbon atoms appears at 190.4 (5t) and 147.8 (4t') ppm, in agreement with those of 4-7. Table 1.…”

“…The formation of the target compounds was confirmed by means of the X-ray diffraction analysis of single crystals of 6 and 7. (13), N(4)-Ir-N(5) = 160.09 (11), N(1)-Ir-C(21) = 177.70 (13).…”

“…The bis-NHC counterparts of complexes 4-7 depicted in Scheme 2 display emissions between 482 and 590 nm with quantum yields in PMMA film and in MeTHF solution between 0.73 and 0.49. 13…”

“…HRMS (ESI+,m/z) 11 (s,1H,Im),5.79 (d,3 JH-H = 7.5, 1H, 1H C6H4). 13 Calcd. for C34H22IrN5: C,58.95;H,3.20;N,10.11.…”

“…Figures 3 and 4show a view of the molecules. The coordination of both pincers around each iridium center gives rise to distorted octahedrons with N(4)-Ir-N(5), C(21)-Ir-N(1), and C(1)-Ir-N(2) angles of 160.3(3), 176.0(3), and 155.8(3)º for 6 and 160.09(11), 177.70(13), and 156.22(13)º for 7. The iridium-aryl5t bond length, Ir-C(21), of 1.931 (8) Å for 6 and 1.938 (3) Å for 7 compare well with those of 2 and 3 and are about 0.1 Å shorter than the iridium-aryl4t' distance, Ir-C(1), of 2.043(10) Å for 6 and 2.023(3) Å for 7.…”