A novel design strategy for deeper blue and more stable thermally activated delayed fluorescent emitters

Thermally activated delayed fluorescent (TADF) materials are considered as the competitive alternative to traditional fluorescent and noble-metal-based phosphorescent materials due to their high electroluminescence (EL) efficiency and low cost. Solution-processable TADF OLEDs have drawn great research attention and can be potentially applied in both flat-panel displays and lighting sources in the near future. However, the blue light emitting TADF materials with high luminance, satisfying color purity and excellent stability are still rare. Herein, two blue light emitting TADF molecules (CzAC-TRZ, DFAC-TRZ) are designed and synthesized. Due to the modified acridine units by introducing 9-phenylcarbazole and dibenzofuran as σ-groups into the molecular skeletons, CzAC-TRZ, DFAC-TRZ possess high energy states and rigid molecular configuration. Solution-processed OLEDs based on CzAC-TRZ and DFAC-TRZ achieved high EL efficiency with the external quantum efficiency (EQE) up to 11.8% and 11.5%, respectively. Moreover, compared with the analogue emitter (DMAC-TRZ) fabricated control devices, CzAC-TRZ and DFAC-TRZ OLEDs presented lower roll-offs, blue-shift and narrower EL spectra. These results have shown that introducing high energy state building blocks into the donor units via σ bonds offers a promising approach of developing stable deeper blue TADF emitters.