A bromine-substituted thermally activated delayed fluorescent (TADF) molecule AQCzBr2 is designed with both small singlet–triplet splitting (DEST) and increased spin–orbit coupling (SOC) to boost intersystem crossing (ISC) for singlet oxygen generation. AQCzBr2 nanoparticles (NPs) demonstrate high productivity of singlet oxygen generation (UD = 0.91) which allows highly efficient photodynamic therapy toward cancer cells.
