The ΔEST values of two conformers were confirmed separately by different excitation wavelength. With an excitation wavelength of 360 nm, the S1 and T1 energies of QAC were calculated to be 2.97 and 2.66 eV, demonstrating a large ΔEST of 0.31 eV. At an excitation wavelength of 420 nm, the S1 and T1 energy levels of a-DMAC-TRZ for QEC were calculated to be 2.79 and 2.59 eV, thus translating to a smaller ΔEST of 0.20 eV. Owing to the effect of the rigid molecular backbone and the degenerate alignment of 3 LE of QAC and 3 CT of QEC for efficient dual fluorescence emission, the resulting OLEDs achieved a high EQEmax of 28.9%