Merchán Manuela, Serrano-Andrés Luis, Robb Michael A, Blancafort Lluís
Instituto de Ciencia Molecular, Universitat de València, Dr. Moliner 50, Burjassot, ES-46100 Valencia, Spain.
J Am Chem Soc. 2005 Feb 16;127(6):1820-5. doi: 10.1021/ja044371h.
We address the possibility of populating the lowest triplet state of cytosine by an "intrinsic"mechanism, namely, intersystem crossing (ISC) along the ultrafast internal conversion pathway of the electronically excited singlet species. For this purpose, we present a discussion of the ISC process and triplet-state reactivity based on theoretical analysis of the spin-orbit strength and the potential energy surfaces for the relevant singlet and triplet states of cytosine. High-level ab initio computations show that ISC is possible in wide regions of the singlet manifold along the reaction coordinate that controls the ultrafast internal conversion to the ground state. Thus, the ISC mechanism documented here provides a possibility to access the triplet state, which has a key role in the photochemistry of the nucleic acid bases.
我们探讨了通过一种“内在”机制使胞嘧啶的最低三重态布居的可能性，即沿着电子激发单重态物种的超快内转换途径进行系间窜越（ISC）。为此，我们基于对胞嘧啶相关单重态和三重态的自旋 - 轨道强度以及势能面的理论分析，对ISC过程和三重态反应性进行了讨论。高水平的从头算计算表明，沿着控制向基态超快内转换的反应坐标，在单重态流形的广泛区域内ISC是可能的。因此，这里记录的ISC机制为进入三重态提供了一种可能性，而三重态在核酸碱基的光化学中起着关键作用。
