One of the key metrics of TADF materials that affects device performance is the rate of RISC. Rapid RISC (large kRISC) implies the efficient harvesting of triplet excitons and their conversion to singlets, outcompeting both intrinsic non-radiative pathways (increasing an OLED's IQE and stability) as well as multi-excitonic quenching pathways such as triplet-triplet annihilation, and thereby alleviating the efficiency roll-off of the external quantum efficiency (EQE) at higher driving current (where triplet exciton density is highest). According to Fermi's Golden rule, the rate of RISC can be expressed according to equation 1: