TPAPyN is a nitroreductase (NTR) responsive type I photosensitizer (photosensitizer). It aids in imaging and image-guided photodynamic therapy (PDT) of hypoxic cancer cells. In aqueous environments, TPAPyN is non-fluorescent, but upon NTR cleavage of the nitrofuran quencher, it regains fluorescence and triggers aggregation-induced emission. TPAPyN serves as a fluorescent probe for hypoxic cancer-specific imaging.