Luminescent Platinum(II) Complexes with Terdentate NCC Ligands

The synthesis, structure, and luminescence of Pt(II) complexes of the type [Pt(N boolean AND C boolean AND C)(L)] are reported, where N boolean AND C boolean AND C is a terdentate ligand resulting from the cycloplatination of 2-(3,5-diphenoxyphenyl)pyridine or 2-(4,4 ''-dimethyl-[1,1 ':3 ',1 ''-terphenyl]-5 '-yl)pyridine, and L represents a monodentate ancillary ligand, which can be gamma-picoline, 4-pyridinecarboxaldehyde, PPh3, n-butyl or 2,6-dimethylphenyl isocyanide, CO, or the N-heterocyclic carbenes 1-butyl-3-methylimidazol-2-ylidene or 4-butyl-3-methyl-1-phenyl-1H-1,2,3-triazol-5-ylidene. Derivatives bearing CO, isocyanides, or carbenes showed the highest stabilities in solution, whereas the pyridine and PPh3 derivatives establish ligand-exchange equilibria in acetonitrile. Different supramolecular structures are observed in the solid state, which largely depend on the nature of the ancillary ligand. Isocyanides and CO favor pi interactions between the aromatic rings, metallophilic PtPt contacts, or a combination of both. In contrast, pyridine ligands may lead to bimolecular assemblies driven by C-HO, C-HPt, or C-H/pi hydrogen bonds. Luminescence was examined in fluid solution, poly(methyl methacrylate) matrices, and the solid state at 298 K, and in 2-methyltetrahydrofuran glasses at 77 K. The majority of derivatives show highly efficient emissions from (ILCT)-I-3/MLCT or (ILCT)-I-3/MLCT/LLCT excited states of monomeric species. The formation of excimers and different types of emissive aggregates are demonstrated, which lead to red-shifted emissions of different origins and characteristics depending on the involved noncovalent interactions.