𝑘 +-#. = 𝑘 -#. 𝑒 :∆3 +1" /?0 (S3) While the two different methods are susceptible to the exact values of different rate constants, some qualitative conclusions may be drawn. In general, using the steady-state fluorescence intensity is a good approximation for TADF compounds with small DES-T (<0.1 eV, Figure ), while using the lifetime of the delayed component as the proxy is more accurate for compounds with larger DES-T (>0.1 eV, Figure ). For 4CzBN, which has a quite large DES-T of 0.28 eV, using only the lifetime of the delayed component as the proxy is likely to yield a very good estimate of FTET. One should however always be careful before employing either method and make sure that the implied assumptions are valid for the particular system.