Bimetallic Platinum(II) Complexes with Bridging Di-NHC and N^C^C Ligands: Synthesis and Photophysical Properties

Three new bimetallic Pt(II) compounds of the type [{Pt(N^C^C)}2{μ-(ImMe)2(CH2)n}] [n = 1 (1), 3 (2), 6 (3)], where N^C^C is the dimetalated terdentate ligand 2-(4,4''-dimethyl-[1,1':3',1''-terphenyl]-5'-yl)pyridine and ImMe is N-methylimidazol-N-yl-2-ylidene, have been synthesized in order to explore their ability to form molecular assemblies that affect their luminescence. Restricted rotation through the Pt-carbene bond gives rise to mixtures of stereoisomers, that hinder the obtention of single crystals. The complexes show efficient emissions with high phosphorescence quantum yields in 2 wt % doped PMMA films (PLQY: 73-77%). Significant modifications of their photophysical properties in fluid solution are observed upon variation of the solvent, with the highest efficiencies found in 2-methyltetrahydrofurane (up to 63% for complex 3). In the case of complex 1, which contains the shortest linkage, the formation of excimers in MeCN and MeOH causes a significant quenching of the emission, with a substantial decrease in the quantum yield.