Many previous studies have evaluated the spectral shift under internal or external electric field by correlating the vertical emission energy (E F ) values with the LUMO-HOMO gap. As shown in Figure , increasing solvent polarity raises the HOMO energy but lowers the LUMO energy, thus decreasing the LUMO-HOMO gap. The variation of HOMO and LUMO energies and the LUMO-HOMO gap as a function of F X was shown in Figure . Under F X , increasing the field strength lowers HOMO energy yet raises LUMO energy, therefore broadening the gap between them. Inverse trends are observed when decreasing F X . Interestingly, a linear relationship is found between the LUMO-HOMO gap and E F in both cases (Figure ). A larger E F corresponds to a larger HOMO-LUMO gap, validating the use of the HOMO-LUMO gap variation to illustrate the change of E F . However, it is noteworthy that the parameters used to fit the data are different between the two cases shown in Figure and 5B. The line in the case of F X (Figure ) has a steeper slope than that in polar solvents (Figure ), indicating different spectral tuning mechanisms. Besides, it is worth noting that the first excited S 1 state still corresponds to the HOMO → LUMO transition under polar solvents (Table ) and within the electric field strength explored (Table ), yet the energy order of frontier orbitals may change in stronger fields due to their different response characteristics, in which case the linear relationship shown in Figure may no longer be valid. A more direct and precise understanding of the change in E F can be obtained by examining the changes in S 0 and S 1 energies, as shown in Figure and. Additionally, since the interaction with electrostatic environments, such as polar solvents or OEEFs, directly correlates with their dipole moments, the energy changes of the S 0 and S 1 states can be easily predicted qualitatively or even quantitatively based on their dipole moments.