Diphosphine ligands, on the other hand, possess dual attributes as effective -donors and -acceptors , rendering them an intriguing choice as ligands. However, heteroleptic copper (I) complexes involving diaminediphosphine ligands confront the challenge of ligand disproportionation in solution, a process whose rate can be exacerbated under irradiation (Figure ). To circumvent this limitation, the choice of ligand can be crucial. Using a sterically demanding phosphine, preferably with a large bite angle, and a relatively less bulky diamine could be the favorable choice of ligands. Additionally, phosphines with large bite angles destabilize the flattening distortion in the excited state thereby enhancing emissive properties of the complex. Heteroleptic diphosphine copper (I) complexes with a di-halo bridge represent ubiquitous precursors in catalysis, owing to their luminescent properties and have been the subject of extensive investigation. The phosphine ligands afford a precise manipulation over the structural architecture of the [Cu(diphos)-X]n species, making them an interesting choice to study the effect of ligands on the photophysical properties of copper (I) complexes (Figure ). Bulky chelating ligands such as dapBz or the ligands possessing larger bite angles such as Josiphos promote the formation of three-coordinated monomeric copper (I) complexes; whereas ligands like BINAP, dppf, dppp, and dppBz facilitate four-coordinated dimeric motif with bridging halides. Additionally, four-coordinate dimeric assemblies, denoted in Figure , are frequently observed, characterized by both halides and bis(phosphines) serving as bridging entities. Such complexes are often associated with flexible ligands possessing large bite angles, as illustrated by [Cu(μ-diop)(μ-X)]2 (X = Cl, I) or CuI complexes incorporating dppb and dppPent ligands.