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 (ψ_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.