Intersystem crossing (ISC) of triplet photosensitizers is a vital process for fundamental photochemistry and photodynamic therapy (PDT). Herein, we report the co‐existence of efficient ISC and long triplet excited lifetime in a heavy atom‐free bodipy helicene molecule. Via theoretical computation and time‐resolved EPR spectroscopy, we confirmed that the ISC of the bodipy results from its twisted molecular structure and reduced symmetry. The twisted bodipy shows intense long wavelength absorption (ϵ=1.76×10⁵ m⁻¹ cm⁻¹ at 630 nm), satisfactory triplet quantum yield (Φ_T=52 %), and long‐lived triplet state (τ_T=492 μs), leading to unprecedented performance as a triplet photosensitizer for PDT. Moreover, nanoparticles constructed with such helical bodipy show efficient PDT‐mediated antitumor immunity amplification with an ultra‐low dose (0.25 μg kg⁻¹), which is several hundred times lower than that of the existing PDT reagents.

中文翻译：

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阐明低剂量光动力治疗螺旋 BODIPY 中的系统间交叉机制。

三重态光敏剂的系间交叉（ISC）是基础光化学和光动力疗法（PDT）的重要过程。在此，我们报道了重原子自由体螺旋烯分子中高效 ISC 和长三线态激发寿命的共存。通过理论计算和时间分辨 EPR 光谱，我们证实了体的 ISC 是由于其扭曲的分子结构和降低的对称性造成的。扭曲体表现出强烈的长波长吸收（ 630 nm 处ϵ =1.76×10 ⁵  m ^-1  cm ^-1）、令人满意的三重态量子产率（Φ _T =52 %）和长寿命的三重态（τ _T =492 μs） ），作为 PDT 的三重态光敏剂具有前所未有的性能。此外，用这种螺旋体构建的纳米粒子在超低剂量（0.25 μg kg ^-1）下表现出有效的PDT介导的抗肿瘤免疫放大作用，比现有PDT试剂低数百倍。