Luminescent Platinum(IV) Complexes Bearing Cyclometalated 1,2,3-Triazolylidene and Bi- or Terdentate 2,6-Diarylpyridine Ligands

The synthesis, structure, and photophysical properties of luminescent Pt-IV complexes that combine cyclometalated 1,2,3-triazolylidene and bi- or terdentate 2,6-diarylpyridine ligands are reported. The targeted complexes represent the first examples of Pt-IV species with a cyclometalated mesoionic aryl-NHC ligand. They exhibit moderate or weak emissions in fluid solution at 298 K arising from (LC)-L-3 states, which become very intense in poly(methyl methacrylate) (PMMA) matrices at 298 K. DFT and TD-DFT calculations confirm that the chromophoric ligand is the cyclometalated 2,6-diarylpyridine and show that the aryl-NHC ligand exerts a beneficial effect on the emission efficiencies of these derivatives by increasing the energy of deactivating LMCT excited states with respect to comparable Pt-IV complexes with cyclometalated 2-arylpyridine ligands.