Transient absorption (TA) spectra of the 0.05 mM and 8 mM samples of TIPS-Pn and TIPS-Tn in anhydrous toluene were collected by exciting the sample at 405 nm and 3.8 mW, with the complete data sets given in Sec. S2 of the supplementary material. Figure summarizes the TA spectra of TIPS-Pn. At both concentrations, a ground-state bleach (GSB) is observed at ∼650 nm, and a small amount of stimulated emission (SE) at ∼720 nm. For the the 0.05 mM TIPS-Pn solution (Fig. (a)), there are additional excited-state absorption (ESA) signals centered at approximately 453, 514, and 572 nm, which are consistent with previous observations of the absorption of the TIPS-Pn singlet exciton. The spectrum of the 0.05 mM TIPS-Pn solution appears to maintain its shape over time. Figure 1(b) shows the averaged spectrum over early times (50-150 ps), and late times (7500-8000 ps), normalized to the GSB. The shape is essentially identical for both time windows, suggesting that predominantly singlet excitons are present over the full 8 ns window, and there is insignificant triplet formation. The kinetics at all wavelengths fit well to a single exponential decay with a lifetime of 18.1 ± 0.2 ns (Fig. and Sec. S4.1 of the supplementary material). A small deviation is present at very early times (<50 ps), which we attribute to solvent reorganization. 17 Previously reported lifetimes of TIPS-Pn singlet excitons vary from around 12 to 22 ns, with this range of values likely due to the presence of additional deactivation pathways in some of these measurements through reactions with oxygen. the fluorescence lifetime of TIPS-Pn was 13.3 ns in air-equilibrated toluene and 22 ns in degassed toluene. The anhydrous samples here should have little oxygen present, which is consistent with the 18 ns lifetime measured for TIPS-Pn here being towards the higher end of the previously reported lifetimes.