Cyclometalated Platinum Complexes with Aggregation-Induced Phosphorescence Emission Behavior and Highly Efficient Electroluminescent Ability

Aggregation-induced emission (AIE) materials can exhibit intense luminescence in the aggregated or solid state, which are highly desirable for OLED application. However, only limited research results on developing AIE-active Pt II complexes in electroluminescence (EL) application have been reported so far. Herein, a series of AIE-active Pt II (C^N)(N-donor ligand)Cl complexes have been developed. Their chemical structures have been determined by NMR, MS, and X-ray crystallography characterization. Theoretical results including the frontier molecular orbitals, the simulated UV–vis spectra, and natural transition orbitals (NTO) have been employed to insightfully interpret their photophysical properties. It has also been found that a much higher degree of molecular aggregation in these Pt II complexes should be required to induce phosphorescent AIE than that for the fluorescent AIE behavior. These AIE-active Pt II complexes can exhibit very strong emission in poly(methyl methacrylate) (PMMA) films with the phosphorescence quantum yield (Φ p ) of ∼72.0%, while that in dilute solution is just about 4.7%. Accordingly, on the basis of these AIE-active Pt II complexes, the optimized OLEDs fabricated by the simple solution-processed strategy can achieve high EL efficiencies with a maximal external efficiency (η ext ) of 28.4%, a maximal current efficiency (η L ) of 75.9 cd A –1, and a maximal power efficiency (η P ) of 62.7 lm W –1 . Considering the rarity for EL investigations of the AIE-active Pt II complexes, the concerned results realized by these Pt II (C^N)(N-donor ligand)Cl complexes should provide valuable clues for exploring AIE-active Pt II phosphorescent complexes with high EL performance.