A fraction of the population of S 1 can decay to the ground state radiatively and both crystals show PF. As mentioned in Section , the MS-CASPT2/aug-cc-pVDZ predicts well the values for fluorescence and emission energies. Using the Einstein equation, we estimated fluorescence rates of 1.7 × 10 8 and 9.9 × 10 7 s -1 for IPA and TPA corresponding to fluorescence lifetimes of 6 and 10 ns (Table ). These values, particularly for TPA, are overestimated compared to the experimental values of 2 and 1 ns. This discrepancy might be related to the absence of excitonic effects in the calculations that could affect the oscillator strengths and the lack of consideration of vibrational effects. Table : Fluorescence (Fl), phosphorescence (Ph), most important (reverse) intersystem crossing (rISC) rate constants (k f and k P , k (r)ISC , and k exc ) computed at 300 K in the IPA and TPA crystals. Section S6 in the SI shows all calculated constants.