Density functional theory (DFT) simulations and time-dependent DFT were performed for TPA-2 before the compound was synthesized. HOMO/LUMO distributions of TPA-2 in the ground state are shown in Fig. . The LUMO of TPA-2 is predominantly located on the acceptor, whereas the HOMO is located on the donor. The separated frontier molecular orbitals lead to extremely small theoretical ΔEST values for TPA-2.