The population dynamics of 2-TP gas , in Figure ), indicates a slower rate of ISC dynamics compared to the solvated models. As in the preceding investigations, this observation can be explained by the energies of the associated adiabatic states. A closer examination of Figure reveals that for the El-Sayed allowed transition, 2-TP gas exhibits a larger ∆E ST than its solvated counterparts. Moreover, the S 2 /S 1 , T 2 /T 1 , and T 3 /T 2 energy gaps in Figure and S5 highlight the existence of energetically distinct states. This reduces the likelihood of vibronically induced strong spin-orbit coupling, which in turn gives rise to the resulting population dynamics. The 3-TP gas model also shows discrepancies from the approximated solvation models. Here, the singlet state dynamics demonstrates a gradual rise in the S 1 population, with T 2 emerging as the predominant triplet state in the 1 ps dynamics. The rationale for this behavior is not straightforward. One potential explanation lies in the significant energy gap between S 4 and the lower singlet states in 3-TP gas . This difference is exemplified in the energies of the valence excited states, as detailed in Table .