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

Area of Science:

• * Photochemistry and Photophysics
• * Materials Science
• * Nanomedicine and Cancer Therapy

Background:

• * Enhancing phototherapeutic efficacy requires strategies to prolong the lifespan of singlet oxygen (¹ O₂ ) particularly under dark and hypoxic conditions.
• * Heavy-atom-free photosensitizers are desirable for reduced toxicity in photodynamic therapy.
• * Boron dipyrromethene (BODIPY) dyes offer tunable photophysical properties for various applications.

Purpose of the Study:

• * To synthesize and evaluate anthracene-functionalized BODIPY dyes as efficient, heavy-atom-free photosensitizers for phototherapy.
• * To investigate the mechanism of reversible singlet oxygen (¹ O₂ ) capture and release for prolonged
• afterglow
• * To assess the in vitro and in vivo efficacy of the developed photosensitizer for cancer treatment.

Main Methods:

• * Synthesis of three BODIPY dyes, with a focus on anthracene-functionalized ABDPTPA.
• * Characterization of photophysical properties, including singlet oxygen (¹ O₂ ) quantum yield and lifetime measurements.
• * In vitro cytotoxicity assays on U87MG cells and in vivo near-infrared-II fluorescence imaging-guided phototherapy in a tumor model.

Main Results:

• * ABDPTPA demonstrated efficient spin-orbit charge-transfer intersystem crossing, yielding a high ¹ O₂ quantum yield (60%).
• * The anthracene moiety reversibly reacted with ¹ O₂ to form an endoperoxide, which upon light cessation, released ¹ O₂ via thermal cycloreversion, creating a prolonged ¹ O₂
• afterglow
• with a half-lifetime of 9.2 minutes.
• * ABDPTPA nanoparticles exhibited low cytotoxicity (IC₅₀ = 3.6 µg mL^-1 on U87MG cells) and effectively inhibited tumor proliferation in vivo with no observed side effects.

Conclusions:

• * Anthracene-functionalized BODIPY (ABDPTPA) serves as an efficient heavy-atom-free photosensitizer.
• * The developed ¹ O₂
• afterglow
• strategy significantly enhances phototherapeutic efficacy.
• * ABDPTPA nanoparticles show great promise for advanced phototheranostics, enabling complete tumor regression.