Aromaticity Tuning of Heavy-Atom-Free Photosensitizers for Singlet Fission-Enhanced Immunogenic Photodynamic Oncotherapy

The quantum yield of reactive oxygen species is of central importance for the development of organic photosensitizers and photodynamic therapy (PDT). A common molecular design approach for optimizing organic photosensitizers involves the incorporation of heavy atoms into their backbones. However, this raises concerns regarding heightened dark cytotoxicity and a shortened triplet-state lifetime. Herein, we demonstrate a heavy-atom-free (HAF) photosensitizer design strategy founded on the singlet fission (SF) mechanism for cancer PDT. Through the "single-atom surgery" approach to deleting oxygen atoms in pyrazino[2,3-