In search of high-performance platinum(II) phosphorescent materials for the fabrication of red electroluminescent devices

The rational design and syntheses of Pt(iqdz)₂ (1) and Pt(pydz)₂ (2) bearing isoquinolinyl indazole (iqdz)H or pyridyl indazole (pydz)H groups on the coordinating ligands are reported. Single-crystal X-ray diffraction studies of 1 reveal a square planar geometry, in which two iqdz ligands adopt a trans-configuration. Short N⋯H contacts (-2.21 Å) are detected between the ortho-hydrogen atom of isoquinoline and the adjacent N atom of the indazole fragment, making the overall molecular geometry analogous to that of the platinum(II) porphyrinato complexes. The lowest absorption bands for both complexes reveal strong state mixings between singlet and triplet (metal-to-ligand charge transfer and intra-ligand) manifolds. This, in combination with the introduction of a camphor-like structure to avoid the stacking effect, leads to phosphorescence with unprecedented brightness both in solution and in the solid state. Organic light-emitting diode (OLED) devices fabricated using 1 as a dopant emitter have been achieved in a multilayer configuration. The results constitute the first highly efficient Pt ^II-based red OLED.