Copper(I) complexes for sustainable light-emitting electrochemical cells

Four prototype heteroleptic copper(I) complexes [Cu(bpy)(pop)][PF6] (bpy = 2,2'-bipyridine, pop = bis (2-(diphenylphosphino) phenyl) ether), [Cu(phen)(pop)][PF6] (phen = 1,10-phenanthroline), [Cu(bpy) (pdpb)][PF6] (pdpb = 1,2-bis(diphenylphosphino) benzene) and [Cu(phen)(pdpb)][PF6] are presented. The synthesis, X-ray structures, solution and solid-state photophysical studies, and the performance in light-emitting electrochemical cells (LECs) of these complexes are described. Their photophysical properties are interpreted with the help of density functional theory (DFT) calculations. The photophysical studies in solution and in the solid-state indicate that these copper(I) complexes show good luminescent properties which allow them to be used as active materials in electroluminescent devices such as LECs. Additionally, these materials are very attractive since we can take advantage of their low-cost, due to the copper abundance, and their limited environmental damaging effects for producing cheap large-area panels based on the LEC technology for lighting applications. LEC devices were fabricated using the four prototype copper(I) complexes together with an ionic liquid (IL), 1-ethyl-3-methylimidazolium hexafluoridophosphate, at a molar ratio of 1 : 1. They yield devices that are comparable to those obtained for most LEC devices based on ruthenium(II) and iridium(III) complexes. Hence, this work shows that promising electroluminescent devices can be prepared using cheap and environmentally friendly copper(I) complexes.