We demonstrate the first evidence of radioactivity-synchronized fluorescence quenching of a near-infrared tight-emitting dye by a radionuclide, Cu-64, and subsequent fluorescence enhancement upon Cu-64 decay to the daughter isotopes Ni-64 and Zn-64. The dynamic switch from high radioactivity and low fluorescence to Low radioactivity and high fluorescence is potentially useful for developing complementary multimodal imaging and detection platforms for chemical, environmental, and biomedical applications as well as for unraveling the mechanisms of meta-induced dynamic fluorescence changes.