(C^C*) Cyclometalated binuclear N-heterocyclic biscarbene platinum(II) complexes--highly emissive phosphorescent emitters.

A series of bimetallic N-heterocyclic carbene (NHC) platinum(II) complexes with the general formula [Pt(NHC)(L)]2Ph were synthesized, which are composed of two [Pt(NHC)(L)] (L = acetylacetone, dipivaloylmethane or dimesitoylmethane; NHC = 3-methylimidazole or 3-benzylimidazole) fragments. Both fragments are cyclometalated to the same central phenyl ring in the para- or meta-position. All complexes have been fully characterized by standard techniques, two of them additionally by solid-state structures. Photoluminescence properties were investigated and very high quantum yields of 76-93% at room temperature have been observed. For a single-matrix device with an emitter concentration of 30%, a current efficiency of 25 cd A(-1), an external quantum efficiency of 8.5%, and a luminance efficiency of 10 lm W(-1) were achieved at 300 cd m(-2). Density functional theory (DFT) calculations were performed to support experimental data and gain further insight into the photoluminescence behaviour.