Cyclometalated (C^C*) platinum(II) N-heterocyclic carbene (NHC) complexes are emerging as a new class of phosphorescent emitters for the application in organic light-emitting devices (OLEDs). We present the synthesis of six new complexes of this class to investigate the influence of extended π systems. Therefore, six different NHC ligands with a varying number of additional phenyl substituents were used in combination with the monoanionic acetylacetonate (acac) ligand to obtain complexes of the general formula [(NHC)Pt(II)(acac)]. The complexes were fully characterized by standard techniques and advanced spectroscopic methods ((195)Pt NMR). For all complexes the solid-state structure determination revealed a square-planar coordination of the platinum atom. Absorption and emission spectra were measured in thin amorphous poly(methyl methacrylate) films at room temperature. Four compounds emit in the blue-green region of the visible spectrum with quantum yields of up to 81%.

Binuclear C^C* cyclometalated NHC platinum(II) compounds with bridging amidinate ligands were synthesized to evaluate their photophysical properties. Their three-dimensional structures were determined by a combination of 2D NMR experiments, mass spectrometry, DFT calculations, and solid-state structure analysis. The bridging amidinate ligands enforce short distances between the platinum centers of the two cyclometalated structures, which gives rise to extraordinary photophysical properties.

Significant improvement of photophysical properties for blue emitting C^C* cyclometalated NHC complexes by changing the acac-ligands.

Cyclometalated platinum(II) complexes with β-diketone ligands have recently attracted increasing interest as phosphorescent emitters for organic light-emitting devices (OLEDs). We present the synthesis of the new cyclometalated Pt(II) N-heterocyclic carbene complex [(NHC)PtII(acac)] (acac = acetylacetonate, NHC = 1-(dibenzo[b,d]thiophen-4-yl)-3-methyl-1H-imidazoyl). The complex was fully characterized by advanced spectroscopic methods (2D NMR, Pt NMR), elemental analysis, and solid-state structure determination, which revealed a square-planar coordination of the platinum atom. The photoluminescence properties were investigated in amorphous poly(methyl methacrylate) (PMMA) thin films. Quantum chemical density functional theory (DFT) computations on the singlet and triplet ground states have shown admixing of the Pt 5d orbitals with the frontier molecular orbitals (FMOs), explaining the good quantum yield.