Changing the Emission Properties of Phosphorescent C not equal to -Cyclometalated Thiazol-2-ylidene Platinum(II) Complexes by Variation of the beta -Diketonate Ligands

• Published in: Chemistry : a European journal Vol. 23; no. 5; pp. 1118 - 1128
• Main Authors: Leopold, Hendrik, Heinemeyer, Ute, Wagenblast, Gerhard, Muenster, Ingo, Strassner, Thomas
• Format: Journal Article
• Language: English
• Published: 01.01.2017
• Subjects: Carbenes; Decay; Emission analysis; Ligands; Organic light emitting diodes; Phosphorescence; Polymethyl methacrylates
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201604456

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 beta -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 beta -diketonate under basic conditions. All the compounds were fully characterised by standard techniques, including super(195)PtNMR spectroscopy. Three solid-state structures revealed quite different aggregation behaviour depending on the beta -diketonate architecture. The reported complexes showed strong phosphorescence at room temperature in amorphous poly(methyl methacrylate) films. The emission wavelengths (ca. 510nm) were found to be independent of the beta -diketonate ligand, but the electronically diverse beta -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 ( super(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, 24.0lmW super(-1) luminous efficacy and 37.8cdA super(-1) current efficiency at 300cdm super(-2). Optimal emission: Seven platinum(II) complexes based on the C not equal to *-cyclometalating thiazol-2-ylidene motif and different beta -diketonate ligands have been synthesised and investigated for their structural and emission properties (see figure). The complexes show strong phosphorescence in PMMA films, the electronically diverse beta -diketonates strongly influencing the observed quantum yields (QY) and decay lifetimes. The most promising complex has additionally been investigated for its performance in OLEDs.