Development of type I photosensitizers (PSs) with strong hydroxyl radical (^·OH) formation is particularly important in the anaerobic tumor treatment. On the other hand, it is challenging to obtain an efficient solid-state intramolecular motion to promote the development of molecular machine and molecular motor. However, the relationship between them is never revealed. In this work, a pyrazine-based near-infrared type I PS with remarkable donor–acceptor effect is developed. Notably, the intramolecular motions are almost maximized by the combination of intramolecular and intermolecular engineering to simultaneously introduce the unlimited bond stretching vibration and boost the group rotation. The photothermal conversion caused by the intramolecular motions is realized with efficiency as high as 86.8%. The D–A conformation of PS can also induce a very small singlet-triplet splitting of 0.07 eV, which is crucial to promote the intersystem crossing for the triplet sensitization. Interestingly, its photosensitization is closely related to the intramolecular motions, and a vigorous motion may give rise to a strong ^·OH generation. In view of its excellent photosensitization and photothermal behavior, the biocompatible PS exhibits a superior imaging-guided cancer synergistic therapy. This work stimulates the development of advanced PS for the biomedical application and solid-state intramolecular motions.

中文翻译：

---

剧烈的分子内运动增强近红外染料中产生强羟基自由基的 I 型光敏作用，实现协同治疗

开发具有强羟基自由基（^· OH）形成的I型光敏剂（PS）在厌氧肿瘤治疗中尤为重要。另一方面，获得高效的固态分子内运动以促进分子机器和分子马达的发展具有挑战性。然而，他们之间的关系却从未被透露。在这项工作中，开发了一种具有显着供体-受体效应的吡嗪基近红外I型PS。值得注意的是，通过分子内和分子间工程的结合，分子内运动几乎最大化，同时引入无限的键伸缩振动并促进基团旋转。实现了分子内运动引起的光热转换，效率高达86.8%。PS的D-A构象还可以诱导0.07 eV的非常小的单线态-三线态分裂，这对于促进三线态敏化的系间跨越至关重要。有趣的是，它的光敏性与分子内运动密切相关，剧烈的运动可能会产生强烈的^· OH生成。鉴于其优异的光敏性和光热行为，生物相容性PS表现出优异的成像引导癌症协同治疗。这项工作促进了先进 PS 在生物医学应用和固态分子内运动方面的发展。