If we allow an ISC rate constant of 3.08 × 10 6 s -1 (or a time constant of 325 ns) on top of the contribution from SF, 3.7 × 10 -9 M of T 1 are produced from ISC, and we obtain a total T 1 concentration of reach the 4.0 × 10 -9 M, or 0.057 mOD T 1 absorption limit, at 8 ns. The actual ISC rate constant therefore must be lower than (or equal to) this value, as a higher value would result in a level of triplet formation that would be observable above the noise level in the TA data.