where 𝑘 S is the sum of the rate constants for ISC (𝑘 ISC ), radiative (𝑘 r S ) and non-radiative (𝑘 nr S ) decay from S 1 , and 𝑘 T is the sum of the rate constants for RISC (𝑘 RISC ), radiative (𝑘 r T ) and non-radiative (𝑘 nr T ) decay from T 1 .