Accordingly, this is a suitable FOM as in fact it relates more directly to the singlet:triplet population ratio. For many TADF materials kISC is substantially faster than 𝑘 ! " , in which case both FOMs will have similar values, but the latter FOM has the advantage that as it directly relates to the triplet population, it should provide better correlation with J90. We can see in Fig. that this FOM does indeed correlate somewhat stronger with J90 (ρ = 0.700) than kRISC (ρ = 0.638).