Changing the Emission Properties of Phosphorescent C

Cyclometalated thiazol-2-ylidene platinum(II) complexes based on the N-phenyl-4,5-dimethyl-1,3-thiazol-2-ylidene N-heterocyclic carbene (NHC) ligand and seven different ß-diketonate ligands have been synthesised and investigated for their structural and photophysical properties. The complexes were synthesised in a one-pot procedure starting with the in situ formation of the corresponding silver(I) carbene and transmetalation to platinum, followed by the reaction with the respective ß-diketonate under basic conditions. All the compounds were fully characterised by standard techniques, including 195 Pt NMR spectroscopy. Three solid-state structures revealed quite different aggregation behaviour depending on the ß-diketonate architecture. The reported complexes showed strong phosphorescence at room temperature in amorphous poly(methyl methacrylate) films. The emission wavelengths (ca. 510 nm) were found to be independent of the ß-diketonate ligand, but the electronically diverse ß-diketonates strongly influence the observed quantum yields (QY) and decay lifetimes. The results of theoretical studies employing density functional theory (DFT) methods support the conclusion of a metal-to-ligand charge transfer (3 MLCT) as the main emission process, in accordance with the reported photophysical properties. Standard organic light-emitting diodes (OLEDs) prepared with unoptimised matrix materials using one of the complexes showed values of 12.3 % external quantum yield, 24.0 lm W-1 luminous efficacy and 37.8 cd A-1 current efficiency at 300 cd m-2 .

Binuclear C

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.

Phosphorescent Platinum(II) Complexes with C

Two C^C* cyclometalated platinum(II) N-heterocyclic carbene (NHC) complexes with the general formula [(C^C*)Pt(O^O)] (C^C*=1-dibenzofuranyl-3-methylbenzimidazolylidene; O^O=dimesitoylmethane) have been synthesized and extensively characterized, including solid-state structure determination, (195) Pt NMR spectroscopy, and 2D NMR (COSY, HSQC, HMBC, NOESY) spectroscopy to elucidate the impact of their structural differences. The two regioisomers differ in the way the dibenzofuranyl (DBF) moiety of the NHC ligand is bound to the metal center, which induces significant changes in their physicochemical properties, especially on the decay time of the excited state. Quantum yields of over 80 % and blue emission colors were measured.

C

Neutral cyclometalated platinum(ii) N-heterocyclic carbene complexes [Pt(C^C*)(O^O)] with C^C* ligands based on 1-phenyl-1,2,4-triazol-5-ylidene and 4-phenyl-1,2,4-triazol-5-ylidene, as well as acetylacetonato (O^O = acac) and 1,3-bis(2,4,6-trimethylphenyl)propan-1,3-dionato (O^O = mesacac) ancillary ligands were synthesized and characterized. All complexes are emissive at room temperature in a poly(methyl methacrylate) (PMMA) matrix with emission maxima in the blue region of the spectrum. High quantum efficiencies and short decay times were observed for all complexes with mesacac ancillary ligands. The sterically demanding mesityl groups of the mesacac ligand effectively prevent molecular stacking. The emission behavior of these emitters is in general independent of the position of the nitrogen in the backbone of the N-heterocyclic carbene (NHC) unit and a variety of substituents in 4-position of the phenyl unit, meta to the cyclometalating bond.

Enlarging the π system of phosphorescent (C

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%.