Changing the Emission Properties of Phosphorescent C^C*-Cyclometalated Thiazol-2-ylidene Platinum(II) Complexes by Variation of the β-Diketonate Ligands.

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 β-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 β-diketonate under basic conditions. All the compounds were fully characterised by standard techniques, including195 Pt NMR spectroscopy. Three solid-state structures revealed quite different aggregation behaviour depending on the β-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 β-diketonate ligand, but the electronically diverse β-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 .