Luminescent [Cu(N^N)(P^P)]X heteroleptic complexes based on 1-H-imidazo-1,10-phenanthroline ligands

A series of six new heteroleptic copper(I) complexes of the [Cu(N^N)(P^P)]⁺ type are reported in which P^P is 4,5-bis(diphenylphosphano)-9,9-dimethylxanthene (xantphos) and N^N are ligands based on 1,10-phenanthroline (phen) with different degrees of steric encumbrance in their 2,9-positions (R = H or CH₃), and varying substitution on their imidazo backbone. The synthesized complexes were fully characterized by NMR spectroscopy, high-resolution mass spectrometry, as well as elemental and single-crystal X-ray analysis. Their electrochemical and photophysical properties were investigated, including supporting theoretical calculations, and HER catalytic investigations were conducted to probe potential reactivity. While the luminescence properties vary across the series in dichloromethane (DCM) and tetrahydrofuran (THF) solvents, selected complexes act as strong emitters, achieving photoluminescence quantum yields of up to 47%. In particular, [Cu(L3b)(xantphos)]PF₆ exhibits a long emission lifetime of 8.52 μs in THF.