Figure shows the absorption and emission spectra of PtOEP, TAB, and DPA along with their molecular structures. TAB has a unique structure with three anthracenes linked via boron in a threedimensionally orthogonal arrangement. TAB was synthesized by a previously reported method. Due to the interaction between the three anthracene moieties, the absorption and fluorescence wavelengths of TAB are red-shifted compared to DPA, which is one of the anthracene monomer derivatives. This is ascribed to a charge-transfer (CT) type transition between HOMO and LUMO as shown by the DFT calculation in Figure . Figure shows the energy levels of the first excited singlet state (S1) and the first excited triplet state (T1) of each molecule. The S1 and T1 energies of PtOEP shown in Figure are based on reported values. PtOEP absorbs green light and exhibits a high ISC yield (𝛷 &'" ≈ 1) due to the heavy atom effect, 39 making its energy relationship with anthracene derivatives suitable for the TTA-UC system. The S1 energies of TAB and DPA were estimated from the intersection of the absorption and fluorescence spectra in Figure , and the S2 energy of TAB was estimated from the edge of the shortwavelength absorption band (400 nm). The T1 energies of TAB (1.76 eV) and DPA (1.73 eV) were calculated using the DFT method (B3LYP-D3/6-311G(d)). For DPA, the calculated T1 energy matches a previously reported calculation and is also close to the experimentally determined value, supporting the overall reliability of the calculated values. The upconversion emission following TET from TAB to DPA was observed, confirming that the T1 energy of TAB is higher than that of DPA (Figure ). From Figure , the TTA is expected to proceed from the T1T1 pair (reactant energy: 3.52 eV) to the S2S0 state (product energy: 3.10 eV) in TAB, while the TTA proceeds to S1S0 (3.04 eV) in DPA.