A Supramolecular Approach for Modulated Photoprotection, Lysosomal Delivery, and Photodynamic Activity of a Photosensitizer.

Prompted by a knowledge of the photoprotective mechanism operating in photosystem supercomplexes and bacterial antenna complexes by pigment binding proteins, we have appealed to a boxlike synthetic receptor (·4Cl) that binds a photosensitizer, 5,15-diphenylporphyrin (), to provide photoprotection by regulating light energy. The hydrophilic renders soluble in water and modulates the phototoxicity of by trapping it in its cavity and releasing it when required. While trapping removes access to the triplet state, a pH-dependent release of diprotonated () restores the triplet deactivation pathway, thereby activating its ability to generate reactive oxygen species. We have employed the -bound complex (⊃) for the safe delivery of into the lysosomes of cancer cells, imaging the cells by utilizing the fluorescence of the released and regulating photodynamic therapy to kill cancer cells with high efficiency.