Analogous fits to the αPh signatures obtained at 7 μJ pulse energy yield an excitation fraction of 2.50 %, close to a linear extrapolation from the excitation fraction obtained from αTp to the pulse energy of the αPh experiment (2.71 %). Thus, the relatively weaker transient signatures of αPh must be due to its predicted lower ring-opening quantum yield ((30 ± 3) % compared to αTp ((58 ± 4) %).