Heavy-atom-free photosensitizers (HAF-PSs) have emerged as a new class of photosensitizers aiming to broaden their applicability and versatility across various fields of the photodynamic therapy of cancers. The strategy involves replacing the exocyclic oxygen atoms of the carbonyl groups of established biocompatible organic fluorophores with sulfur, thereby bathochromically shifting their absorption spectra and enhancing their intersystem crossing efficiencies. Despite these advancements, the photophysical attributes and electronic relaxation mechanisms of many of these HAF-PSs remain inadequately elucidated. In this study, we investigate the excited state dynamics and photochemical properties of two promising HAF-PSs, thio-coumarin and thio-acridone. Employing a combination of steady-state and time-resolved techniques from femtoseconds to microseconds, coupled with quantum chemical calculations, we unravel the electronic relaxation mechanisms that give rise to the efficient population of long-lived and reactive triplet states in these HAF-PSs.

中文翻译：

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硫代吖啶酮和硫代香豆素中的电子弛豫通路：两种吸收可见光的无重原子光敏剂


无重原子光敏剂 （HAF-PS） 已成为一类新型光敏剂，旨在扩大其在癌症光动力治疗各个领域的适用性和多功能性。该策略涉及用硫替换已建立的生物相容性有机荧光团的羰基的外环氧原子，从而在浴变色上改变它们的吸收光谱并提高它们的系统间交叉效率。尽管取得了这些进步，但许多这些 HAF-PS 的光物理特性和电子弛豫机制仍未得到充分阐明。在这项研究中，我们研究了两种有前途的 HAF-PSs——硫代香豆素和硫代吖啶酮的激发态动力学和光化学性质。采用从飞秒到微秒的稳态和时间分辨技术的组合，再加上量子化学计算，我们揭示了电子弛豫机制，这些机制在这些 HAF-PS 中产生了长寿命和反应性三重态的有效种群。