Aggregation-induced phosphorescence emission (AIPE) behaviors in PtII(C^N)(N-donor ligand)Cl-type complexes through restrained D2d deformation of the coordinating skeleton and their optoelectronic properties

Abstract

A series of four-coordinated Pt^II(C^N)(N-donor ligand)Cl-type complexes have been synthesized through combination between C^N-type and N-donor ligands with different sizes. Photophysical features, electrochemical behaviors and electroluminescent (EL) performances have been investigated in detail. Critically, the relationship between the size of organic ligands and aggregation-induced phosphorescence emission (AIPE) behaviors for these Pt^II(C^N)(N-donor ligand)Cl-type complexes has been characterized. With extending the dimensions of the C^N-type and/or N-donor ligands, the AIPE of these Pt^II(C^N)(N-donor ligand)Cl-type complexes is more likely to show up with lower H₂O volumetric fractions (f_w) in the THF solution of these complexes. These unique AIPE experimental results have clearly revealed a new AIE mechanism called restrained D_2d deformation of the coordinating skeleton of these Pt^II(C^N)(N-donor ligand)Cl-type complexes from square-planar (D_4h) in the ground states to the tetrahedron (T_d) skeleton in the excited states. In addition, solution-processed organic light-emitting diodes (OLEDs) based on these AIPE emitters have been fabricated to characterize their EL potential. Impressive EL efficiencies with the maximum external quantum efficiency (η_ext) of 25.2%, current efficiency (η_L) of 53.9 cd A⁻¹ and power efficiency (η_P) of 43.5 lm W⁻¹ can be achieved, indicating great potential of these Pt^II(C^N)(N-donor ligand)Cl-type AIPE emitters in the field of OLEDs. Importantly, this research has proposed a new AIE mechanism to promote the development of new phosphorescent AIPE complexes with great potential in the field of OLEDs.