The substantial steric bulk of the diphosphines prevents the pseudo Jahn Teller distortion in the excited state therefore increasing the excited state lifetimes and luminescence (Figure ). Relative to the [Cu(phen)2] + which is non-luminescent, the [Cu(dmp)2] + and [Cu(phen)(DPEPhos)] + have excited state lifetimes of 85 ns and 190 ns repectively. If both the diamine and diphosphines exhibit high sterically bulk, the lifetimes increase further. 86