Diphosphane-Mediated Control of the Emissive Properties in [Cu(NHC)(P^P)] + Complexes: TADF vs Phosphorescence

The influence of both the skeleton and substituents of the diphosphane in the photophysical properties of [Cu(NHC)(P^P)]PF₆ TADF-phosphorescent emitters is investigated [NHC = Bz-Im-2-XPy (X = H, Cl)]. The study reveals that optimization of the diphosphane structure can boost quantum yields to as high as 85% using carbenes with simple structural frameworks or substituent wings. Remarkably, the diphosphane skeleton emerges as the most influential factor for controlling the quantum yield (Φ). None of the ΔE(S₁-T₁) energy gap, steric factors (buried volume percentage), or T₁ energy alone seem to govern the observed Φ. These insights reveal new avenues for achieving high-performance TADF emitters through ligand engineering.