Trinuclear Cyclometalated Iridium(III) Complex Exhibiting Intense Phosphorescence of an Unprecedented Rate

Abstract

Herein, we present two novel cyclometalated Ir(III) complexes of dinuclear and trinuclear design, Ir 2 (dppm) 3 (acac) 2 and Ir 3 (dppm) 4 (acac) 3 , respectively, where dppm is 4,6-di(4-tert-butylphenyl)pyrimidine ligand and acac is acetylacetonate ligand. In both cases, racdiastereomers were isolated during the synthesis. The materials show intense phosphorescence of outstanding rates (k r = Φ PL /τ) with corresponding radiative decay times of only τ r = 1/k r = 0.36 μs for dinuclear Ir 2 (dppm) 3 (acac) 2 and still shorter τ r = 0.30 μs for trinuclear Ir 3 (dppm) 4 (acac) 3 , as measured for doped polystyrene film samples under ambient temperature. Measured under cryogenic conditions, radiative decay times of the three T 1 substates (I, III, and III) and substate energy separations are τ I = 11.8 μs, τ II = 7.1 μs, τ III = 0.06 μs, ΔE(II−I) = 7 cm −1 , and ΔE(III−I) = 175 cm −1 for dinuclear Ir 2 (dppm) 3 (acac) 2 and τ I = 3.1 μs, τ II = 3.5 μs, τ III = 0.03 μs, ΔE(II−I) ≈ 1 cm −1 , and ΔE(III−I) = 180 cm −1 for trinuclear Ir 3 (dppm) 4 (acac) 3 . The determined T 1 state ZFS values (ΔE(III−I)) are smaller compared to that of mononuclear analogue Ir(dppm) 2 (acac) (ZFS = 210 −1 cm). Theoretical analysis suggests that the high phosphorescence rates in multinuclear materials can be associated with the increased number of singlet states lending oscillator strength to the T 1 → S 0 transition.