A Selenium‐Substituted Heptamethine Cyanine Photosensitizer for Near‐Infrared Photodynamic Therapy

Photodynamic therapy (PDT) is a relatively safe approach to cancer treatment without significant systemic side effects or drug resistance. However, the current PDT efficiency is unsatisfactory due to the lack of near-infrared (NIR) photosensitizers. Heptamethine cyanine (Cy7) dyes are well-known NIR fluorophores and are also used as photosensitizers. But their singlet oxygen quantum yields (ΦΔ ) are not ideal. Herein, we developed an NIR photosensitizer with a long-lived excited triplet state (τ=4.3 μs) by introducing a selenium atom into the structure of a Cy7 dye. The new NIR photosensitizer exhibits a significantly high singlet oxygen quantum yield (ΦΔ =0.11). Its good PDT effect was demonstrated in the living cells. Considering that the selenium-substituted photosensitizer has a very low dark cytotoxicity and good chemical stability, we conclude that it will have a promising future in biomedical and clinical applications.