Hinged and Wide: A New P^P Ligand for Emissive Cu(P^P)(N^N)PF6 Complexes

摘要

Heteroleptic [Cu(BIPHEP)(N^N)][PF ] 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′-Me bpy), have been synthesized and characterized using multinuclear NMR spectroscopies and electrospray ionization mass spectrometry. The single crystal structures of [Cu(BIPHEP)(bpy)][PF ]∙CH Cl , [Cu(BIPHEP)(5,5′-Me bpy)][PF ]∙CH Cl , [Cu(BIPHEP)(6-Mebpy)][PF ]∙Et O∙0.5H O and [Cu(BIPHEP)(6-Etbpy)][PF ] confirm distorted tetrahedral {Cu(P^P)(N^N)} coordination environments. Each compound shows a quasi-reversible Cu /Cu process. In deaerated solution, the compounds are weak emitters. Powdered samples are yellow emitters ( in the range 558–583 nm) and [Cu(BIPHEP)(5,5′-Me bpy)][PF ] 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 < 8 μs, to values of up to 53 μs, consistent with the compounds with N^N = 6-Mebpy, 6-Etbpy and 5,5′-Me bpy exhibiting thermally activated delayed fluorescence (TADF).