There are two important properties of CT excited states from an application viewpoint: significant energy stabilization due to solvation and (2) a small energy gap between the lowest singlet excited state (S1) and the lowest triplet excited state (T1) due to small overlap integral of frontier molecular orbitals. The former is the phenomenon that energies of CT excited states in a solute molecule are stabilized by reorientation of the surrounding solvent molecules. As the permittivity of the solvent increases, the energy of the CT excited state is lowered, and the emission spectrum is redshifted . The latter is the property that the spatial separation of transition orbitals reduces the exchange interaction because the energy separation between the singlet and triplet states is determined by the exchange interaction between orbitals. When the energy gap becomes comparable to the thermal energy of room temperature, reverse intersystem crossing (RISC) from T1 to S1 occurs and TADF is observed . Since the CT excited states have a significant influence on the optical functions of molecules, elucidating the properties and dynamics of CT excited states is of great importance.