The singlet kinetics fit reasonably, with some small deviations which we attribute to solvent reorganization. The bimolecular SF rate constant was fit as (2.7±0.6)×10 9 M -1 s -1 . At the concentration here this value corresponds to a pseudo-first-order rate constant of (2.2 ± 0.5) × 10 7 s -1 , or time constant of 48±10 ns. The lower bound of the SF rate constant corresponds to the fit to the lower bound of the triplet concentration, which comes from the upper bound of the triplet basis spectrum. Correspondingly, the upper bound of the SF rate constant comes from the upper bound of the triplet basis spectrum. The full range of fitted values is summarized in Table of the supplementary material. Dvořák et al. fit the SF rate constant for a range of TIPS-Pn concentrations in chloroform, and found the rate constant decreased linearly with concentration below 10 mM. The bimolecular rate constant from this linear trend was 4 × 10 9 M -1 s -1 . This value is somewhat larger than the (2.7 ± 0.6) × 10 9 M -1 s -1 from our analysis here, which we attribute partly to the different rates of diffusion in chloroform and toluene. Toluene has a higher viscosity than chloroform (0.56 mPas compared with 0.52 mPas), so diffusion is expected to be slower. We can determine a theoretical rate of diffusion in these solvents from the Stokes-Einstein relation as