Solid state luminescence of phosphine-EWO ligands with fluorinated chalcone skeletons and their PdX 2 complexes: metal-promoted phosphorescence enhancement.

Complexes -[PdXL] (X = Cl and Br), where is 1-(PR),2-(CHCH-C(O)Ph)-CF (R = Ph, Cy, and iPr), display phosphorescent emission in the solid state, whereas due to their substantially lower lifetimes, the free ligands exhibit fluorescent behaviour. Alternatively, structurally identical derivatives with halide replaced by CN or Pd replaced by Pt are non-emissive. DFT calculations explain this diverse behaviour, showing that the hybridization of orbitals of the MX moiety with those of the chalcone fragment of ligands is significant only for the LUMO of the emissive compounds. In other words, in our complexes, only MCT processes ( = Metal-perturbed Ligand-centered orbital) lead to observable luminescence.