as the triplet excitons are able to separate easily as molecules diffuse away from each other, and so any intermediate species would be short-lived. The extracted concentrations of S 1 and T 1 of TIPS-Pn from this fit are shown in Fig. (a). The lower bound of the triplet concentration comes from the upper bound of the T 1 basis spectrum. This result corresponds to the upper bound on the S 1 concentration. The yield of triplet excitons at 8 ns was calculated as c T 1 (8 ns)/c S 1 (0 ns) and is between 19 and 27%.