Syntheses and properties of emissive iridium(III) complexes with tridentate benzimidazole derivatives

A series of novel emissive Ir(III) complexes having the coordination environments of [Ir(N boolean AND N boolean AND N)(2)](3+), [Ir(N boolean AND N boolean AND N)-(N boolean AND N)Cl](2+), and [Ir(N boolean AND N boolean AND N)(N boolean AND C boolean AND N)](2+) with 2,6-bis(1-methyl-benzimidazol-2-yl)pyridine (L1, N boolean AND N boolean AND N), 1,3-bis-(1-methyl-benzimidazol-2-yl)benzene (L2H, N boolean AND C boolean AND N), 4'-(4-methylphenyl)-2,2':6',2-terpyridine (ttpy, N boolean AND N boolean AND N), and 2,2'-bipyridine (bpy, N boolean AND N) have been synthesized and their photophysical and electrochemical properties studied. The Ir(III) complexes exhibited phosphorescent emissions in the 500-600 nm region, with lifetimes ranging from approximately 1-10 mu s at 295 K. Analysis of the 0-0 energies and the redox potentials indicated that the lowest excited state of [Ir(L1)(L2)](2+) possessed the highest contribution of (MLCT)-M-3 (MLCT = metal-to-ligand charge transfer) among the Ir(III) complexes, reflecting the sigma-donating ability of the tridentate ligand, ttpy < L1 < L2. The emission quantum yields (Phi) of the Ir(III) complexes ranged from 0.037 to 0.19, and the highest Phi value (0.19) was obtained for [Ir(L1)(bpy)Cl](2+). Radiative rate constants (k(r)) were 1.2 x 10(4) S-1 for [Ir(ttpy)(2)](3+), 3.7 x 10(4) S-1 for [Ir(L1)(bpy)Cl](2+), 3.8 x 10(4) S-1 for [Ir(ttpy)(bpy)Cl](2+), 3.9 X 10(4) S-1 for [Ir(L1)(2)](3+), and 6.6 x 10(4) S-1 for [Ir(L1)(L2)](2+). The highest radiative rate for [Ir(L1)(L2)](2+) With the highest contribution of (MLCT)-M-3 could be explained in terms of the singlet-triplet mixing induced by spin-orbit coupling of 5d electrons in the MLCT electronic configurations.