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

Abstract 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, including 195 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 .