Singlet Oxygen "Afterglow" Therapy with NIR-II Fluorescent Molecules.

Abstract

Improving singlet oxygen (¹ O₂ ) lifespan by fractionated delivery in dark and hypoxic conditions is a better way to achieve enhanced phototherapeutic efficacy. Herein, three boron dipyrromethene (BODIPY) dyes are synthesized to demonstrate that anthracence-functionalized BODIPY, namely ABDPTPA is an efficient heavy-atom-free photosensitizer for the reversible capture and release of ¹ O₂ . The spin-orbit charge-transfer intersystem crossing of ABDPTPA promises a high ¹ O₂ quantum yield of 60% in dichloromethane. Under light irradiation, the anthracene group reacts with ¹ O₂ to produce endoperoxide. Interestingly, after termination of irradiation, the endoperoxide undergoes thermal cycloreversion to produce ¹ O₂ , and regenerates the anthracene module to achieve ¹ O₂ "afterglow," which results in a prolonged half lifetime of ¹ O₂ for 9.2 min. In vitro cytotoxicity assays indicate that ABDPTPA nanoparticles have a low half-maximal inhibitory concentration (IC₅₀ ) of 3.6 µg mL^-1 on U87MG cells. Further, the results of near-infrared-II fluorescence-imaging-guided phototherapy indicate that ABDPTPA nanoparticles can inhibit tumor proliferation even at a low dose (200 µg mL^-1 , 100 µL) without any side effects. Therefore, the study provides a generalized ¹ O₂ "afterglow" strategy to enhance phototheranostics for complete tumor regression.