Heteroleptic, Dinuclear Copper(I) Complexes for Application in Organic Light-Emitting Diodes

A series of highly luminescent, heteroleptic copper(I) complexes has been synthesized using a modular approach based on easily accessible P^N ligands, triphenylphosphine, and copper(I) halides, allowing for an independent tuning of the emission wavelength with low synthetic efforts. The molecular structure has been investigated via X-ray analysis, confirming a dinuclear copper(I) complex consisting of a butterfly shaped metal-halide cluster and two different sets of ligands. The bidentate P^N ligand bridges the two metal centers and can be used to tune the energy of the frontier orbitals and therefore the photophysical characteristics, as confirmed by emission spectroscopy and theoretical investigations, whereas the two monodentate triphenylphosphine ligands on the periphery of the cluster core mainly influence the solubility of the complex. By using electron-rich or electron-poor heterocycles as part of the bridging ligand, emission colors can be adjusted, respectively, between yellow (581 nm) and deep blue (451 nm). These complexes have been further investigated in particular with regard to their photophysical properties in thin films and polymer matrix as well as in solution. Furthermore, the suitability of this class of materials for being applied in organic light-emitting diodes (OLEDs) has been demonstrated in a solution-processed device with a maximum current efficiency of 9 cd/A and a low turn-on voltage of 4.1 V using a representative complex as an emitting compound.