Phosphorescent C∧C Cyclometalated PtII Dibenzofuranyl-NHC Complexes - An Auxiliary Ligand Study

Neutral C∧C* cyclometalated PtII NHC complexes have recently emerged as a new class of phosphorescent emitters with high quantum efficiencies, short decay lifetimes and high thermal stability, which makes them promising candidates for OLED applications. Herein, we report investigations on the photophysical properties of seven new PtII complexes containing a chelating NHC dibenzofuranyl ligand (3‐methyl‐1‐dibenzo[b,d]furan‐4‐ylimidazole) and a bidentate monoanionic auxiliary ligand. All complexes have been fully characterized including extensive NMR studies (COSY, HSQC, HMBC, NOESY, 195Pt NMR), three of them also by solid‐state structures. The extraordinary influence of the auxiliary ligands on the photoluminescence properties is demonstrated by quantum yields ranging from 0 % to 91 % in amorphous PMMA films at room temperature. DFT calculations were performed in order to investigate the nature of the emissive states in more detail. Seven new C∧C* cyclometalated platinum(II) NHC complexes were synthesized. Three were investigated by X‐ray diffraction experiments, and the photoluminescence properties for all were determined. The cyclometalating carbene ligands, with a dibenzofuranyl moiety, were used in combination with different co‐ligands. The importance of the right choice of these often underestimated auxiliary ligands becomes obvious when considering the quantum yields, ranging from 0 to 91 %.