The ground state oxidation potential for the bis-diimine copper (I) complexes spans across +0.50 to +1.00 V vs SCE, while the reduction potential ranges from -1.30 V to -1.80 V vs SCE, indicating their propensity as superior reducing agents i.e. greater tendency of electron donation than acceptance. The heteroleptic diimine diphosphine copper (I) complexes possess analogous reduction potentials (Eºred = -1.30 V to -1.70 V vs SCE). Contrarily, the oxidation potential is way higher; Eºox = +1.10 V to +1.50 V vs SCE (Figure ). This observation stems from a combined effect of lowering of the HOMO by -back bonding effect of diphosphines, as well as destabilization of the square planar geometry of Cu (II) by increasing steric bulk. However, the Beller group demonstrated that as a consequence of Cu-P bond elongation after oxidation, these complexes encounter limitations on stability. The excited state redox potentials can be calculated by the Rehm and Weller equation. Although E0-0 is challenging to determine directly, it can be estimated using either the absorption (Eabs) or emission maxima (Eem) (Figure ). It is worth to note that estimating with Eabs tends to overestimate ΔE0-0, while Eem tends to underestimate it.