Xie Min, Ren Shuang-Xiao, Hu Die, Zhong Ji-Meng, Luo Jie, Tan Yin, Li Yan-Ping, Si Li-Ping, Cao Jun
School of Materials Science and Hydrogen Energy & Guangdong Key Laboratory for Hydrogen Energy Technologies, Foshan University, Foshan, Guangdong, 528000, P. R. China.
School of Medicine, Foshan University, Foshan, Guangdong, 528000, P. R. China.
Phys Chem Chem Phys. 2023 Oct 18;25(40):27756-27765. doi: 10.1039/d3cp03730d.
The substitution of oxygen with chalcogen in carbonyl group(s) of canonical nucleobases gives an impressive triplet generation, enabling their promising applications in medicine and other emerging techniques. The excited-state relaxation S(ππ*) → S(nπ*) → T(ππ*) has been considered the preferred path for triplet generation in these nucleobase derivatives. Here, we demonstrate enhanced quantum efficiency of direct intersystem crossing from S to triplet manifold upon substitution with heavier chalcogen elements. The excited-state relaxation dynamics of sulfur/selenium substituted guanines in a vacuum is investigated using a combination of static quantum chemical calculations and excited-state molecular dynamics simulations. We find that in sulfur-substitution the S state predominantly decays to the S state, while upon selenium-substitution the S state deactivation leads to simultaneous population of the S and T states in the same time scale and multi-state quasi-degeneracy region S/S/T. Interestingly, the ultrafast deactivation of the spectroscopic S state of both studied molecules to the S state occurs through a successive S → S → S path involving a multi-state quasi-degeneracy S/S/S. The populated S and T states will cross the lowest triplet state, and the S → T intersystem crossing happens in a multi-state quasi-degeneracy region S/T/T and is accelerated by selenium-substitution. The present study reveals the influence of both the chalcogen substitution element and initial spectroscopic state on the excited-state relaxation mechanism of nucleobase photosensitizers and also highlights the important role of multi-state quasi-degeneracy in mediating the complex relaxation process. These theoretical results provide additional insights into the intrinsic photophysics of nucleobase-based photosensitizers and are helpful for designing novel photo-sensitizers for real applications.
在标准核碱基的羰基中用硫族元素取代氧可产生令人印象深刻的三线态生成，使其在医学和其他新兴技术中具有广阔的应用前景。激发态弛豫S(ππ*) → S(nπ*) → T(ππ*) 被认为是这些核碱基衍生物中三线态生成的首选途径。在此，我们证明了用较重的硫族元素取代后，从单重态到三线态的直接系间窜越量子效率得到了提高。结合静态量子化学计算和激发态分子动力学模拟，研究了硫/硒取代鸟嘌呤在真空中的激发态弛豫动力学。我们发现，在硫取代的情况下，单重态主要衰减为单重态，而在硒取代的情况下，单重态失活导致在相同的时间尺度和多态准简并区域S/S/T中同时填充单重态和三线态。有趣的是，两个研究分子的光谱单重态到单重态的超快失活是通过涉及多态准简并S/S/S的连续S → S → S路径发生的。填充的单重态和三线态将穿过最低三线态，并且单重态到三线态的系间窜越发生在多态准简并区域S/T/T中，并因硒取代而加速。本研究揭示了硫族元素取代元素和初始光谱态对核碱基光敏剂激发态弛豫机制的影响，也突出了多态准简并在介导复杂弛豫过程中的重要作用。这些理论结果为基于核碱基的光敏剂的内在光物理提供了更多的见解，并有助于设计用于实际应用的新型光敏剂。
