Luminescent and Redox-Active Iridium(III)-Cyclometalated Compounds with Terdentate Ligands

Two novel bis-terdentate Ir(III)-cyclometalated complexes, [Ir(L1)(L1-)]2+ (1) and [Ir(L1-)2]+ (2), have been prepared (L1 is 2,6-bis(7′-methyl-4′-phenyl-2′-quinolyl)pyridine; L1- is its mono-anion, see Figure 1). To the best of our knowledge, 1 and 2 are the first luminescent and redox-active Ir(III)-cyclometalated bis-terdentate compounds. In acetonitrile solution, on oxidation, 2 undergoes a reversible, metal-centered, one-electron oxidation at +1.40 V, whereas 1 does not exhibit any oxidation process up to +2.00 V. On reduction, both compounds undergo four reversible ligand-centered one-electron processes. The absorption spectra of the compounds are dominated by moderately intense (ε in the 103-104 M- cm-1 range) spin-allowed metal-to-ligand charge-transfer (MLCT) bands at wavelengths longer than 350 nm and by intense (ε in the 104-105 M-1 cm-1 range) ligand-centered (LC) bands at shorter wavelengths. The complexes exhibit an intense luminescence both at 77 K in MeOH/EtOH, 4:1 (v/v), rigid matrix (1, λmax = 592 nm, τ = 20 μs; 2, λmax = 598 nm, τ = 9 μs) and at room temperature in deoxygenated acetonitrile solution (1, λmax = 620 nm, τ = 325 ns, Φ = 0.005; 2, λmax = 630 nm, τ = 2.3 μs, Φ = 0.066). In all cases, the emission is assigned to triplet MLCT levels (namely, Ir → L1 and Ir → L1- in 1 and 2, respectively).