However, further reduction of DEST does not significantly change kRISC/kISC, i.e., there does not seem to be a benefit of reducing DEST below 0.1 eV. Notably, a small DEST usually requires a highly twisted molecular structure, which also leads to weak oscillator strength for the S0-S1 transition and thus to a low 𝑘 ! " . Here we note, that DEST is only a reflection of the energy gap between the S1 and T1 states as measured spectroscopically and, as neither intermediate states nor vibronic interactions are captured by this metric, it thus is frequently an overestimation of the energy barrier for RISC. 29