Heteroleptic [Cu(P^P)(N^N)][PF6] compounds with isomeric dibromo-1,10-phenanthroline ligands

A series of [Cu(P^P)(N^N)][PF6] compounds are reported in which N^N is 2,9-dibromo-1,10-phenanthroline (2,9-Br2phen), 3,8-dibromo-1,10-phenanthroline (3,8-Br2phen) or 4,7-dibromo-1,10-phenanthroline (4,7-Br2phen) and P^P is bis(2-(diphenylphosphano)phenyl)ether(POP) or 4,5-bis(diphenylphosphano)-9,9-dimethylxanthene(xantphos). The compounds have been characterized by solution multinuclear NMR spectroscopy, mass spectrometry and single-crystal X-ray analysis. Each compound undergoes a partially-reversible or irreversible copper-centred oxidation, the highest potential being for 2,9-Br2phen-containing compounds. In solution, the compounds are weak yellow or orange emitters, whereas powdered samples exhibit yellow emissions with photoluminescence quantum yields of up to 45% for [Cu(xantphos)(2,9-Br2phen)][PF6] with an excited state lifetime τ1/2= 9.9 μs. Values of λemmaxfor [Cu(POP)(2,9-Br2phen)][PF6] and [Cu(xantphos)(2,9-Br2phen)][PF6] are blue-shifted with respect to compounds with the 3,8- and 4,7-isomers, both in solution and the solid state