Phosphorescent Platinum(II) Complexes Based on C∧C Cyclometalating Aryltriazol-5-ylidenes

Two series of heteroleptic platinum(II) carbene compexes of the type [Pt(C∧C*)(O∧O)] (O∧O = acetylacetonate) with C∧C* cyclometalated 4-phenyl-1,2,4-triazol-5-ylidene as well as 1-phenyl-1,2,4-triazol-5-ylidene ligands were prepared. The effect of various substituents in the 4-position of the phenyl ring (4-phenyltriazole: H, Cl, OCH3, NO2; 1-phenyltriazole: H, Cl, OCH3, CH3) was studied. The ligand precursors were obtained by quaternization of the corresponding aryl-1,2,4-triazoles with iodomethane. The complexes were synthesized by a reaction sequence starting from the triazolium precursors via the silver(I) carbenes, transmetalation with dichloro(1,5-cyclooctadiene)platinum(II), cyclometalation reaction, and finally addition of acetylacetonate. All complexes have been characterized by standard techniques such as 1H NMR, 13C NMR, and elemental analysis. Additionally, solid-state structures of seven complexes could be obtained by single-crystal X-ray diffraction. According to absorption and emission spectra, the complexes reveal interesting photophysical properties with strong emissions in the blue region of the visible spectrum at room temperature, which are sensitive to the donor and acceptor properties of the substituents at the cyclometalating ligand.