The upper bound of k ISC for TIPS-Pn is greater than the pseudo-first-order SF rate constant (k SF [S 0 ]) up to a concentration of 1.45 mM, where k ISC and k SF [S 0 ] are equal. Based on the kinetic model and these rate constants, at 8 mM, ISC could account for up to 10% of triplets formed after 8 ns. So the assumption of negligible ISC made when fitting the bimolecular SF rate above is potentially invalid. We therefore refit the model with k ISC equal to 3.08 × 10 6 s -1 and found that for this level of ISC, k SF fits to lower range of (2.5 ± 0.6) × 10 9 M -1 s -1 (compared to (2.7 ± 0.6) × 10 9 M -1 s -1 for no ISC) (Table ). This analysis is shown in detail in Sec. S4.2.2 of the supplementary material. The fit to the deconvoluted TA data at both 0.05 mM and 8 mM using these rate constants is given in Fig. . We emphasize that this fit only uses an upper bound of ISC; the true ISC rate constant may be significantly lower. Considering the uncertainty in the ISC rate constant, the range of bimolecular SF rate constants becomes 1.9×10 9 M -1 s -1 (lower bound of T 1 concentration, upper bound of ISC) to 3.3×10 9 M -1 s -1 (upper bound of T 1 concentration, no ISC), or (2.6 ± 0.7) × 10 9 M -1 s -1 . Using the lower bound of this adjusted rate at 0.05 mM results in a revised 2.4 × 10 -10 M of T 1 formed due to SF, which is still substantially lower than the limit of detection, and does not affect the upper bound of the ISC rate constant determined here.