Introducing sterically demanding substituents and π-π-interactions into [Cu(P∧P)(N∧N)]+ complexes

A series of ten N<^>N chelating ligands based on a 2,2 '-bipyridine (bpy) metal-binding domain and featuring sterically hindering substituents in the 6- and 6,6 '-positions has been synthesized and characterized. The ligands have been incorporated into a family of 15 heteroleptic complexes of type [Cu(P<^>P)(N<^>N)][PF6] where P<^>P is the wide bite-angle bisphosphane ligand bis(2(diphenylphosphanyl)phenyl)ether (POP) or (9,9-dimethyl-9H-xanthene-4,5-diyl)bis(diphenylphosphane) (xantphos). Substituents in several of the N<^>N ligands ligands possess phenyl rings remotely tethered to enable intra- and intermolecular pi-pi-interactions in the [Cu(P<^>P)(N<^>N)](+) cations. Single crystal X-ray structures of 12 complexes are reported. The effects of the functional groups in the bpy ligand on the photophysical properties of the complexes have been studied; solid-state emission maxima range from 518 to 567 nm. Values of the solid-state photoluminescence quantum yields (PLQYs) of the [Cu(P<^>P)(N<^>N)][PF6] compounds respond to the nature of the N<^>N ligand. In general, we observed that the [Cu(P<^>P)(N<^>N)](+) complexes containing 6,6 '-disubstituted complexes with phenyl moieties connected via a CH2CH2 or CH2CH2CH2 spacer to the bpy domain have the highest values of PLQY. The most significant compounds are [Cu(POP)((2-PhEt)(2)bpy)][PF6] (PLQY = 67%) and [Cu(POP)((3-PhPr)(2)bpy)][PF6] (PLQY = 72%) where (2-PhEt)(2)bpy = 6,6 '-bis(2-phenylethyl)-2,2 '-bipyridine and (3-PhPr)(2)bpy = 6,6 '-bis(3-phenylpropyl)-2,2 '-bipyridine. These PLQY values are among the best performing previously reported families of [Cu(P<^>P)(N<^>N)][PF6] compounds.