We developed a family of four orange-to-red TADF compounds whose structures differ by the number of nitrogen atoms containing within the conjugated acceptor core. The structure-property relationship among the four compounds has been systematically investigated using DFT calculations, and a combination of photophysical and electrochemical studies; OLEDs were also fabricated using these materials as emitters. It was found that increasing the nitrogen atom content in the in the acceptor (BP) of the D-A typed compounds results in a more stabilized LUMO, smaller ΔEST and faster kRISC. In particular, having a nitrogen at the 10-position of BP notably enhances kRISC, as demonstrated in