Bimetallic platinum( <scp>ii</scp> ) complexes with bridging di-NHC and N^C^C ligands: synthesis and photophysical properties

Three new bimetallic Pt(II) compounds of the type [{Pt(dmtppy)}₂{μ-(Im_Me)₂(CH₂)_<i>n</i>}] [<i>n</i> = 1 (1), 3 (2), 6 (3)], where dmtppy is the dimetalated tridentate N^C^C ligand 2-(4,4''-dimethyl-[1,1':3',1''-terphenyl]-5'-yl)pyridine and Im_Me is <i>N</i>-methylimidazol-<i>N</i>-yl-2-ylidene, have been synthesized in order to explore their ability to form molecular assemblies that affect their luminescence. Restricted rotation around the Pt-carbene bond leads to mixtures of atropisomers, which hinder the growth of single crystals. The complexes show efficient emissions with high phosphorescence quantum yields in 2 wt% doped PMMA films at 298 K (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% quantum yield 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.