SRE-II, an amide derivative, serves as an activatable photosensitizer tailored for photodynamic cancer research, exhibiting diminished fluorescence and photosensitizing properties. Upon carboxylesterase-catalyzed amide bond cleavage, it transforms into its active form, SDU Red. In light-exposed environments, SRE-II prompts DNA damage and induces cell apoptosis, highlighting its potential as a theranostic agent for triple-negative breast cancer [1].