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.