Synthesis, properties, and LED performance of highly luminescent metal complexes containing indolizino[3,4,5-ab]isoindoles

We report the synthesis, X-ray structures, optical and electrochemical properties, as well as fabrication of light-emitting devices for complexes which have cyclometalated ligands, pin (2-pyridin-2-yl-indolizino[3,4,5-ab]isoindole) and qin (2-quinolin-2-yl-indolizino[3,4,5-ab]isoindole). The new complexes are [Ir(L₁)_3−x(L₂)_x], [Pt(L₁)(L₂)], and [Pd(L₁)(L₂)] (L₁ = pin, qin; L₂ = acac (acetylacenato), pic (2-pyridinecarboxylato); x = 0, 1). The Ir and Pt complexes are highly luminescent, even at room temperature, and the relative luminescence quantum efficiencies are as high as 61%. The Pd complexes exhibit luminescence in the solid state, but the luminescence was quenched in solution. The X-ray crystal structures of Pt(pin)(acac), Pd(qin)(acac) and Pd(qin)(acac) were also obtained. The brightness of the light-emitting device reached values as high as 1.4 × 10⁴ cd/m² and Ir(pin)₃ emits beautiful green light.