Femtosecond Intersystem Crossing in the DNA Nucleobase Cytosine.
Femtosecond Intersystem Crossing in the DNA Nucleobase Cytosine.
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DOI：
10.1021/jz301312h
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发表时间：
2012-10
期刊：
影响因子：
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通讯作者：
Martin Richter;P. Marquetand;J. González-Vázquez;I. Sola;L. González
中科院分区：
文献类型：
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作者：
Martin Richter;P. Marquetand;J. González-Vázquez;I. Sola;L. González
采用从头算分子动力学方法，包括非绝热耦合和自旋轨道耦合，研究了胞嘧啶在吸收紫外光后的失活过程。研究发现，系统间交叉（ISC）在数十飞秒内直接与内部转换竞争，从而使胞嘧啶成为迄今为止计算出的三重态数量最快的有机化合物。研究发现，单重态和三重态之间的密切简并可以超过补偿非常小的自旋轨道耦合，导致有效的ISC。ISC过程的飞秒性质突出了其在光化学中的重要性，并挑战了传统观点，即需要大的单重态-三重态耦合才能有效地进入三重态。这些发现对于理解DNA的光稳定性以及有机分子的光化学和动力学具有重要意义。
Ab initio molecular dynamics including nonadiabatic and spin-orbit couplings on equal footing is used to unravel the deactivation of cytosine after UV light absorption. Intersystem crossing (ISC) is found to compete directly with internal conversion in tens of femtoseconds, thus making cytosine the organic compound with the fastest triplet population calculated so far. It is found that close degeneracy between singlet and triplet states can more than compensate for very small spin-orbit couplings, leading to efficient ISC. The femtosecond nature of the ISC process highlights its importance in photochemistry and challenges the conventional view that large singlet-triplet couplings are required for an efficient population flow into triplet states. These findings are important to understand DNA photostability and the photochemistry and dynamics of organic molecules in general.