Segarra-Martí Javier, Tran Thierry, Bearpark Michael J
Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, White City Campus, 80 Wood Lane, W12 0BZ, London, UK.
Phys Chem Chem Phys. 2019 Jul 14;21(26):14322-14330. doi: 10.1039/c8cp07189f. Epub 2019 Jan 30.
In this article we characterise the radiationless decay of the first few electronic excited states of the cations of DNA/RNA nucleobases uracil and thymine, including the effects of dynamic electron correlation on energies and geometries (optimised with XMS-CASPT2). In both systems, we find that one state of n and another two of π character can be populated following photoionisation, and their different minima and interstate crossings are located. We find strong similarities between uracil and thymine cations: with accessible conical intersections suggesting that depopulation of their electronic excited states takes place on ultrafast timescales in both systems, suggesting that they are photostable in agreement with previous theoretical (uracil) evidence. We find that dynamic electron correlation separates the energy levels of the "3-state" conical intersection (D/D/D) previously located with CASSCF for uracil, which will therefore have a different geometry and higher energy. Simulating the electronic and vibrational absorptions allows us to characterise spectral fingerprints that could be used to monitor these cation photo-processes experimentally.
在本文中，我们描述了DNA/RNA核碱基尿嘧啶和胸腺嘧啶阳离子的前几个电子激发态的无辐射衰变，包括动态电子相关对能量和几何结构的影响（用XMS-CASPT2进行优化）。在这两个体系中，我们发现光离子化后可以填充一个n态和另外两个π态，并且确定了它们不同的极小值和态间交叉点。我们发现尿嘧啶和胸腺嘧啶阳离子之间有很强的相似性：可及的锥形交叉表明它们的电子激发态在超快时间尺度上发生去填充，这表明它们与之前的理论（尿嘧啶）证据一致，具有光稳定性。我们发现动态电子相关分离了之前用CASSCF确定的尿嘧啶“三态”锥形交叉（D/D/D）的能级，因此它将具有不同的几何结构和更高的能量。模拟电子和振动吸收使我们能够表征可用于通过实验监测这些阳离子光过程的光谱指纹。
