A rational design strategy for red thermally activated delay fluorescence emitter employing 2,1,3-benzothiadiazole skeleton with asymmetric structure

Abstract

Organic light-emitting diodes (OLEDs) employing thermally activated delayed fluorescence (TADF) can effectively utilize triplet excitons without the noble-metal doping. However, there are challenges in the design of adjusting the competition between the narrow band gap and the non-radiative transition of red TADF emitters. Herein, a red emitter named as 4-(3,5-di(9H-carbazol-9-yl)phenyl)-7-(9,9-dimethylacridin-10(9H)-yl)benzo[c] [1,2,5]thiadiazole (BCZ-BTD-AD) with an asymmetric structure containing 2,1,3-benzothiadiazole (BTD) as the electron-acceptor, 9,10-dihydro-9,9-dimethylacridin and 1,3-di(9H-carbazol-9-yl)benzene as the electron-donors was designed and synthesized. The twisted conformation and large rigid plane endow the compound TADF and aggregation-induced emission (AIE) characteristics, as well as a high thermal decomposition temperature (Td) of 419 °C. Pure red non-doped OLED (device A) shows the maximum emission peak at 652 nm with the commission internationale de l'eclairage (CIE) coordinates of (0.63, 0.32), the turn-on voltage (Von) of 3.6 V, the maximum brightness (Lmax) of 1728.9 cd m−2, the maximum current efficiency (ηC) of 1.6 cd A−1, the maximum power efficiency (ηP) of 1.2 lm W−1 and the maximum external quantum efficiency (ηext) of 2.3%. Doped OLED (device B) constructed based on BCZ-BTD-AD doped 20% in CBP shows performance with the maximum emission peak of 628 nm, the CIE coordinates of (0.53, 0.37), the turn-on voltage of 3.2 V, the maximum brightness of 1883.9 cd m−2, the maximum current efficiency of 6.8 cd A−1, the maximum power efficiency of 5.0 lm W−1 and the maximum external quantum efficiency of 5.6%.