Strategically Formulating Aggregation-Induced Emission-Active Phosphorescent Emitters by Restricting the Coordination Skeletal Deformation of Pt(II) Complexes Containing Two Independent Monodentate Ligands

Aggregation-induced emission (AIE)-active phosphorescent emitters have intrinsic advantages in time-gated imaging/sensing and improving the electroluminescent efficiencies of organic light-emitting devices (OLEDs). However, compared with the very prosperous and fruitful developments of AIE-active fluorescent emitters and related working mechanisms, the progresses on AIE-active phosphorescent emitters and associated AIE mechanisms are still relatively slow. Herein, the AIE properties of a series of phosphorescent Pt(II) complexes with two monodentate ligands are reported. Compared with the conventional rigid Pt(II) complexes bearing two bidentate ligands or one tri-/tetradentate ligand, the incorporation of two monodentate ligands provides the resulting Pt(II) complexes with more room to deform their coordination skeletons from the square-planar geometry in the ground state to the quasi-tetrahedral configuration in the excited state, causing poor solution emissions. In doped films and aggregate states, intense emissions are observed for these Pt(II) complexes. The as-fabricated solution-processed OLED exhibits an impressively high external quantum efficiency of 21.7%. This study provides an effective way to develop excellent AIE-active phosphorescent emitters.