Unraveling the role of the external electric field on the photo-physical properties of thermally activated delayed fluorescence

Density functional theory (DFT) calculations were performed to understand the effect of the external electric field (EEF) on the essential photo-physical properties of phenozazine-triphenyltriazine (PXZ-TRZ) emitter. Interestingly, the increases in ΔEST values were equally observed under EEFx/y/z = 5.0 × 106 V/cm due to the significant changes in molecular and electronic structures in T1 state. Moreover, spin-orbit couplings (SOCs) under EEFz = 5.0 × 105 V/cm and EEFy/z = 5.0 × 106 V/cm were tremendously augmented, whereas the SOC extremely decreased in the presence of EEFy = 5.0 × 105 V/cm and EEFx = 5.0 × 106 V/cm. Correspondingly, the calculated reverse intersystem crossing rate (kRISC) values are drastically improved in the presence of the EEFy/z = 5.0 × 106 V/cm. On the other hand, the effects of the EEFx = 5.0 × 106 V/cm and EEFy = 5.0 × 105 V/cm on the kRISC were determined to be disadvantageous. Consequently, our theoretical study clearly informs that the role of EEF on the photo-physical properties of TADF materials should be importantly considered as one of the determinants for characterizing TADF materials in the solid-state device.