An upper bound on the rate constant of ISC for TIPS-Tn was determined in a similar manner to that for TIPS-Pn. The TA noise level was determined to be 0.016 mOD, so the maximum triplet absorption at 8 ns is 0.049 mOD. Using the lower bound of the T 1 basis spectrum, this absorption corresponds to a triplet concentration of 1.6 × 10 -8 M (5.2% of the initial S 1 population). This value is higher than for TIPS-Pn, potentially because the T 1 absorption is both less intense and less distinct from S 1 for TIPS-Tn triplets than for TIPS-Pn triplets, or because some triplets actually form over 8 ns, which contribute to the measured noise. Modeling the 0.05 mM concentration without ISC using a bimolecular SF rate constant of 2.0×10 9 M -1 s -1 gives a T 1 concentration of 3.6×10 -10 M, corresponding to an absorbance of 0.001 mOD (supplementary material Fig. ).