For TIPS-Tn, the singlet decay rate constant, k S 1 , was fixed to 1/12.7 ns -1 (taken from the relaxation lifetime of the singlet excited state in the dilute solution in Sec. S4.1 of the supplementary material) minus the ISC and SF contributions (k ISC and k SF × 0.05 mM). The triplet decay rate constant was fixed to 1/80 µs -1 , taken from the lifetime used by Dover et al.. Again, the triplet lifetime is substantially longer than the timescales measured here, and has little effect on the fit.