Hinged and Wide: A New P^P Ligand for Emissive [Cu(P^P)(N^N)][PF 6] Complexes

Molecules. 2019 Oct 31;24(21):3934. doi: 10.3390/molecules24213934.

Abstract

Heteroleptic [Cu(BIPHEP)(N^N)][PF6] complexes (BIPHEP = 1,1'-biphenyl-2,2'-diylbis(diphenylphosphane)), in which N^N is 2,2'-bipyridine (bpy), 6-methyl-2,2'-bipyridine (6-Mebpy), 6-ethyl-2,2'-bipyridine (6-Etbpy), or 5,5'-dimethyl-2,2'-bipyridine (5,5'-Me2bpy), have been synthesized and characterized using multinuclear NMR spectroscopies and electrospray ionization mass spectrometry. The single crystal structures of [Cu(BIPHEP)(bpy)][PF6]∙CH2Cl2, [Cu(BIPHEP)(5,5'-Me2bpy)][PF6]∙CH2Cl2, [Cu(BIPHEP)(6-Mebpy)][PF6]∙Et2O∙0.5H2O and [Cu(BIPHEP)(6-Etbpy)][PF6] confirm distorted tetrahedral {Cu(P^P)(N^N)} coordination environments. Each compound shows a quasi-reversible Cu+/Cu2+ process. In deaerated solution, the compounds are weak emitters. Powdered samples are yellow emitters (λemmax in the range 558-583 nm) and [Cu(BIPHEP)(5,5'-Me2bpy)][PF6] exhibits the highest photoluminescence quantum yield (PLQY = 14%). On cooling to 77 K (frozen 2-methyloxolane), the emission maxima are red-shifted and the excited state lifetimes increase from τ1/2 < 8 μs, to τ1/2 values of up to 53 μs, consistent with the compounds with N^N = 6-Mebpy, 6-Etbpy and 5,5'-Me2bpy exhibiting thermally activated delayed fluorescence (TADF).

Keywords: 2,2′-bipyridine; TADF; X-ray structure; bis(phosphane); copper(I); photophysics.

MeSH terms

  • Carbon-13 Magnetic Resonance Spectroscopy
  • Coordination Complexes / chemical synthesis
  • Coordination Complexes / chemistry*
  • Copper / chemistry*
  • Electrochemistry
  • Ligands
  • Luminescence
  • Models, Molecular
  • Proton Magnetic Resonance Spectroscopy
  • Solutions
  • X-Ray Diffraction

Substances

  • Coordination Complexes
  • Ligands
  • Solutions
  • Copper