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, rac-diastereomers 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.