Figure shows the Jablonski diagram of the TTA-UC system composed of two photosensitizers and two emitters. The T1 energy of PtOEP is higher than those of DPA and TAB, indicating that the TET reactions from PtOEP to DPA or TAB occur exothermically. Additionally, because the S1 energies of DPA and TAB are lower than twice of their respective T1 energies, the conditions required for them to function as TTA-UC systems are satisfied when both DPA and TAB are used as TTA emitters. Compared to the TTA-UC material composed of PtOEP and DPA, the PtOEP/TAB system exhibits a smaller anti-Stokes shift. This is because the distributions of electron densities in the HOMO and LUMO of TAB molecule extend over two or three anthracene moieties via the boron atom (Figure ) to cause a charge-transfer (CT) character, resulting in a lowered S1 energy level. Determination of 𝒌 𝐓𝐓𝐀 using Time-Resolved Photolumines- cence Measurements