However, in both systems, population of singlet states from T 1 seems unlikely due to the significant energy gaps. Nevertheless, we observe that when considering higher triplet states, such as T 2 and T 3 , the rates for rISC can be one to two order of magnitudes faster than competing phosphorescence. Previous works highlight the relevant role of the higher-lying triplets in the rISC mechanism in organic systems. In cases where the energy gap between the T/S pair undergoing reverse ISC is substantial, intermediate triplet states can mediate this process. Vibronic interactions between closely spaced triplet states can promote internal conversion between them, effectively lowering the activation energy required for reverse ISC. Our hypothesis is that T 2 in IPA and T 3 in TPA lie very close in energy to T 1 and T 2 , respectively, which should facilitate seamless population transfer between these states.