Benzoylfuran- and Thiophene-Based Thermally Activated Delayed Fluorescence Emitters for Organic Light-Emitting Diodes

Thermally activated delayed fluorescent (TADF) emitters have received much attention in organic light-emitting diodes (OLEDs) due to a number of advantages, including 100% internal quantum efficiency, no heavy-metal doping, and the ability to prevent shortages of conventional fluorescent and phosphorescent materials. Herein, we report two TADF emitters, namely, [3,5-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl](furan-2-yl)methanone (2BFu-mTCz) and [3,5-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl](thiophen-2-yl)methanone (2BTp-mTCz). The emission maxima of the emitters have been observed in the sky-blue region, which are well in accordance with theoretical (density functional theory and time-dependent density functional theory) calculations. The singlet-triplet energy gap (Delta E ST) of the emitters shows the TADF nature due to the small Delta E ST values (Delta E ST = 0.09 eV for 2BFu-mTCz and 0.12 eV for 2BTp-mTCz). Compared with the solution state, the photoluminescence quantum yield increased significantly in the solid state, reaching 40% for 2BFu-mTCz and 46% for 2BTp-mTCz. The maximum external quantum efficiency of 9.6 and 9.0% and sky-blue emission with Commission internationale de l'eclairage coordinates of (0.19, 0.36) and (0.20, 0.36) were observed for 2BFu-mTCz and 2BTp-mTCz, respectively. This work paves a direction to finetune the k RISC values and lifetimes by introducing the heavy atom in direct conjugation.