State-specific heavy-atom effect on intersystem crossing processes in 2-thiothymine: A potential photodynamic therapy photosensitizer
State-specific heavy-atom effect on intersystem crossing processes in 2-thiothymine: A potential photodynamic therapy photosensitizer
复制标题
2-硫胸腺嘧啶系统间交叉过程的状态特异性重原子效应：一种潜在的光动力治疗光敏剂
DOI：
10.1063/1.4776261
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发表时间：
2013-01-28
影响因子：
4.4
通讯作者：
Fang, Wei-hai
中科院分区：
文献类型：
--
作者：
Cui, Ganglong;Fang, Wei-hai
硫胸苷作为光敏剂在肿瘤光动力治疗中具有潜在的应用价值。作为硫代胸腺嘧啶的发色团，2-硫代胸腺嘧啶表现出到最低三重态T-1（约1.5 μ m）的系间跃迁的量子产率。100%），这与天然胸腺嘧啶的激发态行为形成对比，天然胸腺嘧啶通过超快内部转换到基态来耗散多余的电子能量。本文采用高能级完全活动空间自洽场及其二阶微扰方法研究了2-硫代胸腺嘧啶模型的物理机制。我们优化了低7个电子态的最低能量结构，以及10个交叉点。在计算势能分布和自旋轨道耦合的基础上，我们提出了三个竞争性的，有效的非绝热路径，从最初的单重态S-2的最低的三重态T-1。所提出的机械论方案很好地解释了最近的实验现象。胸腺嘧啶和2-硫代胸腺嘧啶之间的独特的生物物理行为的起源归因于重原子效应，这是显着增强，在后者。此外，这种重原子效应被发现是特定的状态，这可以在原则上被用来调整2-硫代胸腺嘧啶的电子物理。本文的高水平电子结构计算也有助于理解硫代胸苷在光动力治疗中的作用机理。(C)2013年美国物理学会。[http：//dx.doi.org/10.1063/1.4776261]
Thiothymidine has a potential application as a photosensitizer in cancer photodynamic therapy (PDT). As the chromophore of thiothymidine, 2-thiothymine exhibits ultrahigh quantum yield of intersystem crossing to the lowest triplet state T-1 (ca. 100%), which contrasts with the excited-state behavior of the natural thymine that dissipates excess electronic energy via ultrafast internal conversion to the ground state. In this work, we employed high-level complete-active space self-consistent field and its second-order perturbation methods to explore the photophysical mechanism of a 2-thiothymine model. We have optimized the minimum energy structures in the low-lying seven electronic states, as well as ten intersection points. On the basis of the computed potential energy profiles and spin-orbit couplings, we proposed three competitive, efficient nonadiabatic pathways to the lowest triplet state T-1 from the initially populated singlet state S-2. The suggested mechanistic scenario explains well the recent experimental phenomena. The origin responsible for the distinct photophysical behaviors between thymine and 2-thiothymine is ascribed to the heavy-atom effect, which is significantly enhanced in the latter. Additionally, this heavy-atom effect is found to be state-specific, which could in principle be used to tune the photophysics of 2-thiothymine. The present high-level electronic structure calculations also contribute to understand the working mechanism of thiothymidine in PDT. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4776261]