An Efficient Heterodinuclear Ir(III)/Pt(II) Complex: Synthesis, Photophysics and Application in Light-Emitting Electrochemical Cells
We report on the design, synthesis, characterization and successful application of a heterodinuclear Ir(III)/Pt(II) complex endowed with two 4,6-diphenylpyrimidine ligands and two acetylacetonate ligands, with one of the former being the rigid bridging unit between the two metal centers. The heterodinuclear complex exhibits red phosphorescence with a high quantum yield of ΦPL=85 % and a short room-temperature phosphorescent decay time of τ=640 ns in toluene solution. The high efficiency of the spin-forbidden T1→S0 transition is demonstrated to originate in a strong spin-orbit coupling of the T1 state with a manifold of excited singlet states, which is manifested in the record-breaking zero-field splitting of the T1 state of 240 cm-1. The high-solubility and non-ionic heterodinuclear complex was employed as the emissive guest compound in a host-guest light-emitting electrochemical cell, and such optimized devices delivered vibrant red emission (λpeak = 615 nm) with a second-fast turn-on and a high external quantum efficiency of 2.7 % at a luminance of 265 cd/m2.