Molecular Engineering for Shortening the Pt???Pt Distances in Pt(II) Dinuclear Complexes and Enhancing the Efficiencies of these Complexes for Application in Deep-Red and Near-IR OLEDs

Deep-red (DR)-to-near-infrared (NIR) phosphorescent organic light-emitting diodes (OLEDs) have potentials for application in various fields ranging from phototherapy to sensing. Accordingly, herein, phenylpyridazine-based bidentate ligands are synthesized and subsequently utilized for the preparation of dinuclear Pt(II) complexes (1-6). The molecular structures of 1-3 is investigated by single-crystal X-ray diffraction, and the results suggest that these complexes have substantially shortened Pt center dot center dot center dot Pt distances (2.906-2.911 angstrom). Complexes 1-6 exhibit intense emissions in the NIR region (700-726 nm), high photoluminescence quantum yield (PLQY) (0.11-0.18), and short phosphorescence decay lifetimes (tau = 0.64-0.95 mu s) in a CH2Cl2 solution. To examine the effect of N-substitution on the dinuclear Pt complexes, the phenylpyrimidine-based Pt(II) emitters 7 and 8 are prepared and discovered to have Pt center dot center dot center dot Pt distances of 2.933 angstrom. 7 and 8 demonstrate strong emissions in the 628-650 nm range with high PLQY of 0.52-0.65. Theoretical studies indicate that the functional groups or atoms in the ligands play crucial roles in the formation of emitters with significantly shortened Pt center dot center dot center dot Pt distances. 3 and 7 are employed as non-doped emitters to fabricate NIR OLEDs, and the resulting OLEDs exhibit electroluminescence peaks at 754 and 692 nm with maximum external quantum efficiencies of 3.0 and 4.4%, respectively.