Teaching an old acceptor new tricks: rationally employing 2,1,3-benzothiadiazole as input to design a highly efficient red thermally activated delayed fluorescence emitter

The exploitation of blue to orange emissive thermally activated delayed fluorescence (TADF) materials has been conducted comprehensively, while the equally important red TADF materials have been studied at a relatively slow pace. Three D-A-D structured fluorescent molecules, N⁴,N⁴,N⁷,N⁷-tetraphenylbenzo[c][1,2,5]thiadiazole-4,7-diamine (BTZ-DPA), 4,7-bis(9H-carbazol-9-yl)benzo[c][1,2,5]thiadiazole (BTZ-CZ) and 4,7-bis(9,9-dimethylacridin-10(9H)-yl) benzo[c][1,2,5]thiadiazole (BTZ-DMAC) were designed and synthesized by rationally employing 2,1,3-benzothiadiazole as an acceptor. The introduction of 2,1,3-benzothiadiazole not only presents an efficient input for the design of red TADF emitters, but also provides benefits for the resulting high-efficiency organic light-emitting diodes (OLEDs) which show a maximum external quantum efficiency of 8.8% at a luminance of 1.06 cd m⁻² with the emission peak at 636 nm.